Reflective circular polarizer for head-mounted display

ABSTRACT

Techniques disclosed herein relate to folded optical systems for near-eye display. In one embodiment, an optical device includes a first polarizer, a second polarizer, and a partial reflector positioned between the first polarizer and the second polarizer. The first polarizer is configured to polarize incident light into light of a first circular polarization state. The second polarizer is configured to transmit light of a second circular polarization state and reflect light of the first circular polarization state without changing its polarization state. The partial reflector is configured to transmit light from the first polarizer, and reflect light from the second polarizer. The light reflected by the partial reflector and the light from the second polarizer have different polarization states.

BACKGROUND

An artificial reality system, such as a head-mounted display (HMD) orheads-up display (HUD) system in the form of a headset or a pair ofglasses, generally includes a near-eye display configured to presentcontent to a user via an electronic or optic display within, forexample, about 10-20 mm in front of the user's eyes. The near-eyedisplay may display virtual objects or combine images of real objectswith virtual objects, as in virtual reality (VR), augmented reality(AR), or mixed reality (MR) applications. For example, in an AR system,a user may view both images of virtual objects (e.g., computer-generatedimages (CGIs)) and the surrounding environment by, for example, seeingthrough transparent display glasses or lenses (often referred to asoptical see-through) or viewing displayed images of the surroundingenvironment captured by a camera (often referred to as videosee-through).

The near-eye display system may include an optical system configured toform an image of a computer-generated image on an image plane. Theoptical system of the near-eye display may relay the image generated byan image source (e.g., a display panel) to create a virtual image thatappears to be away from the image source and further than just a fewcentimeters away from the eyes of the user. For example, the opticalsystem may collimate the light from the image source or otherwiseconvert spatial information of the displayed virtual objects intoangular information to create a virtual image that may appear to be faraway. The optical system may also magnify the image source to make theimage appear larger than the actual size of the image source. In manycases, the applications of artificial reality systems are limited dueto, for example, the cost, size, weight, limited field of view, smalleye box, or poor efficiency of the optical systems used to relay theimages generated by the image source.

SUMMARY

This disclosure relates generally to folded optical systems for near-eyedisplay. A reflective circular polarizer (CP) may be used in a foldedoptical system to replace a reflective linear polarizer and a wave platethat are aligned, thus avoiding the alignment of the reflective linearpolarizer and the wave plate. The reflective circular polarizer canreflect circularly polarized light while keeping the handedness of thereflected light the same as that of the incident light. The reflectivecircular polarizer can be made using, for example, cholesteric liquidcrystal (CLC).

In some embodiments, an optical device may include a first polarizerconfigured to polarize incident light into light of a first circularpolarization state, a second polarizer configured to transmit light of asecond circular polarization state and reflect light of the firstcircular polarization state (where the light reflected by the secondpolarizer may be in the first circular polarization state), and apartial reflector positioned between the first polarizer and the secondpolarizer, where the partial reflector may be configured to transmitlight from the first polarizer and reflect light from the secondpolarizer. The light reflected by the partial reflector and the lightfrom the second polarizer may have different polarization states.

In some embodiments of the optical device, at least one of the firstpolarizer, the second polarizer, or the partial reflector may be on acurved surface. In some embodiments, the curved surface may be a surfaceof an optical lens.

In some embodiments of the optical device, the second polarizer mayinclude a cholesteric liquid crystal (CLC) circular polarizer, where theCLC circular polarizer may include liquid crystal molecules arranged ina helical structure. In some embodiments, the helical structure mayinclude two or more pitches. In some embodiments, the CLC circularpolarizer may include a plurality of layers, each layer having adifferent reflection wavelength range. In some embodiments, each of theplurality of layers may include a helical structure having a differentpitch. In some embodiments, at least two layers of the plurality oflayers may be doped with a chiral dopant material at different dopantconcentrations or may be doped with different chiral dopant materials.In some embodiments, the pitch of the helical structure variesgradually. The CLC circular polarizer may include double-twistcholesteric liquid crystal layers or liquid crystal polymer layers. Insome embodiments, the helical structure may include a left-handedhelical structure, and the second polarizer may be configured totransmit right-handed circularly polarized light and reflect left-handedcircularly polarized light. In some embodiments, the helical structuremay include a right-handed helical structure, and the second polarizermay be configured to transmit left-handed circularly polarized light andreflect right-handed circularly polarized light. In some embodiments ofthe optical device, the first polarizer may include a cholesteric liquidcrystal (CLC) circular polarizer, which may include liquid crystalmolecules arranged in a helical structure.

According to some embodiments, a method of displaying images may includepolarizing light from an image source into light of a first circularpolarization state by a first polarizer, transmitting the light of thefirst circular polarization state to a second polarizer by a partialreflector, reflecting the light of the first circular polarization stateback to the partial reflector (in the first circular polarization state)by the second polarizer, reflecting the light of the first circularpolarization state into light of a second circular polarization stateback to the second polarizer by the partial reflector, and transmittingthe light of the second circular polarization state to a user's eye bythe second polarizer. In some embodiments, the second polarizer mayinclude a cholesteric liquid crystal (CLC) reflective circularpolarizer.

According to some embodiments, a near-eye display device may include adisplay configured to emit display light, a first polarizer configuredto polarize the display light into light of a first circularpolarization state, a second polarizer configured to transmit light of asecond circular polarization state to a user's eye and reflect light ofthe first circular polarization state into light of the first circularpolarization state, and a partial reflector positioned between the firstpolarizer and the second polarizer, the partial reflector configured totransmit light from the first polarizer and reflect light from thesecond polarizer, where the light reflected by the partial reflector andthe light from the second polarizer may have different polarizationstates.

In some embodiments, the near-eye display device may further include anoptical lens having a non-zero optical power, where at least one of thefirst polarizer, the second polarizer, or the partial reflector may beon a surface of the optical lens. In some embodiments, the display mayinclude a transparent display configured to transmit ambient light, andthe near-eye display device may be configured to transmit both theambient light and the display light to the user's eye. The secondpolarizer may include a cholesteric liquid crystal (CLC) reflectivecircular polarizer.

According to some embodiments, a near-eye display device may include adisplay including an output surface, where the display may be configuredto emit display light through the output surface. The output surface maybe configured to at least partially reflect light incident on the outputsurface from an exterior of the display, where the reflected light andthe light incident on the output surface from the exterior of thedisplay may have different polarization states. The near-eye displaydevice may also include a reflective circular polarizer formed on theoutput surface of the display and including liquid crystal moleculesarranged in a helical structure. The reflective circular polarizer maybe configured to reflect light of a first circular polarization state inthe display light back to the output surface of the display, where thereflected light from the reflective circular polarizer to the outputsurface of the display is in the first circular polarization state. Thereflective circular polarizer may also be configured to transmit lightof a second circular polarization state in the display light to a user'seye.

This summary is neither intended to identify key or essential featuresof the claimed subject matter, nor is it intended to be used inisolation to determine the scope of the claimed subject matter. Thesubject matter should be understood by reference to appropriate portionsof the entire specification of this disclosure, any or all drawings, andeach claim. The foregoing, together with other features and examples,will be described in more detail below in the following specification,claims, and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Illustrative embodiments are described in detail below with reference tothe following figures.

FIG. 1 is a simplified block diagram of an example of an artificialreality system environment including a near-eye display according tocertain embodiments.

FIG. 2 is a perspective view of an example of a near-eye display devicein the form of a head-mounted display (HMD) device for implementing someof the examples disclosed herein.

FIG. 3 is a perspective view of a simplified example of a near-eyedisplay device in the form of a pair of glasses for implementing some ofthe examples disclosed herein.

FIG. 4 illustrates an example of an optical see-through augmentedreality system using a waveguide display according to certainembodiments.

FIG. 5 is a cross-sectional view of an example of a near-eye displayaccording to certain embodiments.

FIG. 6 illustrates an example of an optical system for near-eye displayaccording to certain embodiments.

FIG. 7 illustrates an example of an optical system for near-eye displayaccording to certain embodiments.

FIG. 8 depicts an embodiment of a folded-lens system according tocertain embodiments.

FIG. 9 illustrates an embodiment of a folded-lens system according tocertain embodiments.

FIG. 10 illustrates an embodiment of a cholesteric liquid crystalcircular polarizer with left-handed helixes according to certainembodiments.

FIG. 11 illustrates an embodiment of a cholesteric liquid crystalcircular polarizer with right-handed helixes according to certainembodiments.

FIG. 12A illustrates an embodiment of a cholesteric liquid crystal basedcircular polarizer with right-handed helixes according to certainembodiments.

FIG. 12B illustrates the reflection of circularly polarized light by aglass or metal mirror.

FIG. 13 illustrates normalized selective reflection spectra of anexample of an helical cholesteric structure according to certainembodiments.

FIG. 14 illustrates an example of a folded-lens system including areflective circular polarizer according to certain embodiments.

FIG. 15A illustrates an example of a folded-lens system including areflective circular polarizer and operating in a display mode accordingto certain embodiments.

FIG. 15B illustrates an example of a folded-lens system including areflective circular polarizer and operating in a see-through modeaccording to certain embodiments.

FIG. 16 illustrates transmission spectra of three examples of CLClayers.

FIG. 17A illustrates an example of a folded-lens system configured tooperate with a first optical power according to certain embodiments.

FIG. 17B illustrates an example of a folded-lens system configured tooperate with a second optical power according to certain embodiments.

FIG. 18 is a simplified flow chart illustrating an example of a methodof displaying images at multiple image planes using a switchablecircular polarizer according to certain embodiments.

FIG. 19 is a simplified flow chart illustrating an example of a methodof operating a near-eye display device in a display mode and asee-through mode according to certain embodiments.

FIG. 20 is a simplified block diagram of an example of an electronicsystem of a near-eye display according to certain embodiments.

The figures depict embodiments of the present disclosure for purposes ofillustration only. One skilled in the art will readily recognize fromthe following description that alternative embodiments of the structuresand methods illustrated may be employed without departing from theprinciples, or benefits touted, of this disclosure.

In the appended figures, similar components and/or features may have thesame reference label. Further, various components of the same type maybe distinguished by following the reference label by a dash and a secondlabel that distinguishes among the similar components. If only the firstreference label is used in the specification, the description isapplicable to any one of the similar components having the same firstreference label irrespective of the second reference label.

DETAILED DESCRIPTION

Techniques disclosed herein relate generally to folded optics innear-eye display. According to some embodiments, a reflective circularpolarizer (CP) may be used in the folded optics to replace a reflectivelinear polarizer and a wave plate that are aligned, thus avoiding thealignment of the reflective linear polarizer and the wave plate. Thereflective circular polarizer may be configured to reflect light of afirst circular polarization state (e.g., left-handed or right-handedcircular polarization) while keeping the handedness of the reflectedlight same as that of the incident light. The reflective circularpolarizer may transmit light of a second circular polarization statewithout changing its polarization state. Display light from a displaydevice can be polarized into light of the first circular polarizationstate, which may keep its polarization state while it pass through a50/50 mirror and is reflected by the reflective circular polarizer backto a 50/50 mirror. The 50/50 mirror may reflect the light of the firstcircular polarization state into light of the second circularpolarization state back to the reflective circular polarizer. Thereflective circular polarizer may then let the light of the secondcircular polarization state reflected from the 50/50 mirror to passthrough with little or no loss. In this way, display light of the firstcircular polarization state from the display device may be folded by theoptical system and reach the user's eye as light of the secondpolarization state.

In some embodiments, the reflective circular polarizer may beimplemented using cholesteric liquid crystal. The polarization state ofthe light being reflected may be determined by the handedness of thecholesteric helical superstructure formed by the liquid crystalmolecules. Multiple layers of cholesteric liquid crystal may be used toimprove the reflectivity of the reflective circular polarizer. Layers ofcholesteric liquid crystal with different pitches (or periods) may beused to reflect light of different wavelengths.

In addition, the orientation (or alignment) of the liquid crystalmolecules in the reflective circular polarizer may be changed orrealigned by applying an voltage signal on the reflective circularpolarizer, such that the liquid crystal molecules may align with theelectrical field to transmit light of any polarization. As such, theoperation of the HMD may be switched between the display mode (withreflection by the reflective circular polarizer) and the see-throughmode (without reflection by the reflective circular polarizer) byapplying voltages with different levels or polarities.

In one embodiment, when no voltage is applied to the reflective circularpolarizer, display light may be polarized to a first circularpolarization state (e.g., left-handed or right-handed) using, forexample, a circular polarizer. The display light of the first circularpolarization state may pass through a partial reflection mirror, such asa 50/50 mirror, and then be reflected back to the 50/50 mirror by thereflective circular polarizer without changing the polarization state ofthe reflected light. The 50/50 mirror may reflect the display light ofthe first circular polarization state into light of a second circularpolarization state (e.g., right-handed or left-handed) that can betransmitted by the reflective circular polarizer. Thus, the reflectivecircular polarizer may help to fold the light in the display mode toproject the displayed image on an image plane. When a voltage signal isapplied on the reflective circular polarizer, the liquid crystalmolecules may be aligned with the electrical field, and thus light ofany polarization state can pass through without being folded. In thisway, the folded optics can be used for both the display mode and thesee-through mode without compromising the quality of the image in thesee-through mode.

According to certain embodiments, two reflective circular polarizers anda partial reflection mirror, such as a 50/50 mirror or a partial mirrorwith a reflectivity greater than or less than 50%, may be used to changethe optical power of a folded optical device. For example, when novoltage is applied to the reflective circular polarizer, light of afirst circular polarization state may pass through the first reflectivecircular polarizer and the 50/50 mirror and reach the second reflectivecircular polarizer, which may reflect the light of the first circularpolarization state back to the 50/50 mirror. The 50/50 mirror mayreflect the display light of the first circular polarization state intolight of a second circular polarization state that can be transmitted bythe reflective circular polarizer. Thus, the folded optical device mayfold the light of the first circular polarization state, and thus mayhave a first optical power for light of the first circular polarizationstate in the display light. When a voltage signal is applied across atleast one of the two reflective circular polarizers, the liquid crystalmolecules within the reflective circular polarizer may be aligned withthe electrical field, and thus light of any polarization state can passthrough the reflective circular polarizer without being folded. Thus,the folded optical device may have a second optical power when thevoltage signal is applied. In this way, the folded optical device mayachieve different optical powers to relay images on different imageplanes.

In the following description, for the purposes of explanation, specificdetails are set forth in order to provide a thorough understanding ofexamples of the disclosure. However, it will be apparent that variousexamples may be practiced without these specific details. For example,devices, systems, structures, assemblies, methods, and other componentsmay be shown as components in block diagram form in order not to obscurethe examples in unnecessary detail. In other instances, well-knowndevices, processes, systems, structures, and techniques may be shownwithout necessary detail in order to avoid obscuring the examples. Thefigures and description are not intended to be restrictive. The termsand expressions that have been employed in this disclosure are used asterms of description and not of limitation, and there is no intention inthe use of such terms and expressions of excluding any equivalents ofthe features shown and described or portions thereof. The word “example”is used herein to mean “serving as an example, instance, orillustration.” Any embodiment or design described herein as “example” isnot necessarily to be construed as preferred or advantageous over otherembodiments or designs.

I. Near-Eye Display

FIG. 1 is a simplified block diagram of an example of an artificialreality system environment 100 including a near-eye display 120 inaccordance with certain embodiments. Artificial reality systemenvironment 100 shown in FIG. 1 may include near-eye display 120, anoptional external imaging device 150, and an optional input/outputinterface 140 that may each be coupled to an optional console 110. WhileFIG. 1 shows example artificial reality system environment 100 includingone near-eye display 120, one external imaging device 150, and oneinput/output interface 140, any number of these components may beincluded in artificial reality system environment 100, or any of thecomponents may be omitted. For example, there may be multiple near-eyedisplays 120 monitored by one or more external imaging devices 150 incommunication with console 110. In some configurations, artificialreality system environment 100 may not include external imaging device150, optional input/output interface 140, and optional console 110. Inalternative configurations, different or additional components may beincluded in artificial reality system environment 100.

Near-eye display 120 may be a head-mounted display that presents contentto a user. Examples of content presented by near-eye display 120 includeone or more of images, videos, audios, or some combination thereof. Insome embodiments, audios may be presented via an external device (e.g.,speakers and/or headphones) that receives audio information fromnear-eye display 120, console 110, or both, and presents audio databased on the audio information. Near-eye display 120 may include one ormore rigid bodies, which may be rigidly or non-rigidly coupled to eachother. A rigid coupling between rigid bodies may cause the coupled rigidbodies to act as a single rigid entity. A non-rigid coupling betweenrigid bodies may allow the rigid bodies to move relative to each other.In various embodiments, near-eye display 120 may be implemented in anysuitable form factor, including a pair of glasses. Some embodiments ofnear-eye display 120 are further described below with respect to FIGS.2, 3, and 20. Additionally, in various embodiments, the functionalitydescribed herein may be used in a headset that combines images of anenvironment external to near-eye display 120 and artificial realitycontent (e.g., computer-generated images). Therefore, near-eye display120 may augment images of a physical, real-world environment external tonear-eye display 120 with generated content (e.g., images, video, sound,etc.) to present an augmented reality to a user.

In various embodiments, near-eye display 120 may include one or more ofdisplay electronics 122, display optics 124, and an eye-tracking unit130. In some embodiments, near-eye display 120 may also include one ormore locators 126, one or more position sensors 128, and an inertialmeasurement unit (IMU) 132. Near-eye display 120 may omit any of theseelements or include additional elements in various embodiments.Additionally, in some embodiments, near-eye display 120 may includeelements combining the function of various elements described inconjunction with FIG. 1.

Display electronics 122 may display or facilitate the display of imagesto the user according to data received from, for example, console 110.In various embodiments, display electronics 122 may include one or moredisplay panels, such as a liquid crystal display (LCD), an organic lightemitting diode (OLED) display, a micro light emitting diode (mLED)display, an active-matrix OLED display (AMOLED), a transparent OLEDdisplay (TOLED), or some other display. For example, in oneimplementation of near-eye display 120, display electronics 122 mayinclude a front TOLED panel, a rear display panel, and an opticalcomponent (e.g., an attenuator, polarizer, or diffractive or spectralfilm) between the front and rear display panels. Display electronics 122may include pixels to emit light of a predominant color such as red,green, blue, white, or yellow. In some implementations, displayelectronics 122 may display a three-dimensional (3D) image throughstereo effects produced by two-dimensional panels to create a subjectiveperception of image depth. For example, display electronics 122 mayinclude a left display and a right display positioned in front of auser's left eye and right eye, respectively. The left and right displaysmay present copies of an image shifted horizontally relative to eachother to create a stereoscopic effect (i.e., a perception of image depthby a user viewing the image).

In certain embodiments, display optics 124 may display image contentoptically (e.g., using optical waveguides and couplers) or magnify imagelight received from display electronics 122, correct optical errorsassociated with the image light, and present the corrected image lightto a user of near-eye display 120. In various embodiments, displayoptics 124 may include one or more optical elements, such as, forexample, a substrate, optical waveguides, an aperture, a Fresnel lens, aconvex lens, a concave lens, a filter, or any other suitable opticalelements that may affect image light emitted from display electronics122. Display optics 124 may include a combination of different opticalelements as well as mechanical couplings to maintain relative spacingand orientation of the optical elements in the combination. One or moreoptical elements in display optics 124 may have an optical coating, suchas an anti-reflective coating, a reflective coating, a filteringcoating, or a combination of different optical coatings.

Magnification of the image light by display optics 124 may allow displayelectronics 122 to be physically smaller, weigh less, and consume lesspower than larger displays. Additionally, magnification may increase afield of view of the displayed content. The amount of magnification ofimage light by display optics 124 may be changed by adjusting, adding,or removing optical elements from display optics 124.

Display optics 124 may also be designed to correct one or more types ofoptical errors, such as two-dimensional optical errors,three-dimensional optical errors, or a combination thereof.Two-dimensional errors may include optical aberrations that occur in twodimensions. Example types of two-dimensional errors may include barreldistortion, pincushion distortion, longitudinal chromatic aberration,and transverse chromatic aberration. Three-dimensional errors mayinclude optical errors that occur in three dimensions. Example types ofthree-dimensional errors may include spherical aberration, comaticaberration, field curvature, and astigmatism.

Locators 126 may be objects located in specific positions on near-eyedisplay 120 relative to one another and relative to a reference point onnear-eye display 120. In some implementations, console 110 may identifylocators 126 in images captured by external imaging device 150 todetermine the artificial reality headset's position, orientation, orboth. A locator 126 may be a light emitting diode (LED), a corner cubereflector, a reflective marker, a type of light source that contrastswith an environment in which near-eye display 120 operates, or somecombinations thereof. In embodiments where locators 126 are activecomponents (e.g., LEDs or other types of light emitting devices),locators 126 may emit light in the visible band (e.g., about 380 nm to750 nm), in the infrared (IR) band (e.g., about 750 nm to 1 mm), in theultraviolet band (e.g., about 10 nm to about 380 nm), in another portionof the electromagnetic spectrum, or in any combination of portions ofthe electromagnetic spectrum.

External imaging device 150 may generate slow calibration data based oncalibration parameters received from console 110. Slow calibration datamay include one or more images showing observed positions of locators126 that are detectable by external imaging device 150. External imagingdevice 150 may include one or more cameras, one or more video cameras,any other device capable of capturing images including one or more oflocators 126, or some combinations thereof. Additionally, externalimaging device 150 may include one or more filters (e.g., to increasesignal to noise ratio). External imaging device 150 may be configured todetect light emitted or reflected from locators 126 in a field of viewof external imaging device 150. In embodiments where locators 126include passive elements (e.g., retroreflectors), external imagingdevice 150 may include a light source that illuminates some or all oflocators 126, which may retro-reflect the light to the light source inexternal imaging device 150. Slow calibration data may be communicatedfrom external imaging device 150 to console 110, and external imagingdevice 150 may receive one or more calibration parameters from console110 to adjust one or more imaging parameters (e.g., focal length, focus,frame rate, sensor temperature, shutter speed, aperture, etc.).

Position sensors 128 may generate one or more measurement signals inresponse to motion of near-eye display 120. Examples of position sensors128 may include accelerometers, gyroscopes, magnetometers, othermotion-detecting or error-correcting sensors, or some combinationsthereof. For example, in some embodiments, position sensors 128 mayinclude multiple accelerometers to measure translational motion (e.g.,forward/back, up/down, or left/right) and multiple gyroscopes to measurerotational motion (e.g., pitch, yaw, or roll). In some embodiments,various position sensors may be oriented orthogonally to each other.

IMU 132 may be an electronic device that generates fast calibration databased on measurement signals received from one or more of positionsensors 128. Position sensors 128 may be located external to IMU 132,internal to IMU 132, or some combination thereof. Based on the one ormore measurement signals from one or more position sensors 128, IMU 132may generate fast calibration data indicating an estimated position ofnear-eye display 120 relative to an initial position of near-eye display120. For example, IMU 132 may integrate measurement signals receivedfrom accelerometers over time to estimate a velocity vector andintegrate the velocity vector over time to determine an estimatedposition of a reference point on near-eye display 120. Alternatively,IMU 132 may provide the sampled measurement signals to console 110,which may determine the fast calibration data. While the reference pointmay generally be defined as a point in space, in various embodiments,the reference point may also be defined as a point within near-eyedisplay 120 (e.g., a center of IMU 132).

Eye-tracking unit 130 may include one or more eye-tracking systems. Eyetracking may refer to determining an eye's position, includingorientation and location of the eye, relative to near-eye display 120.An eye-tracking system may include an imaging system to image one ormore eyes and may optionally include a light emitter, which may generatelight that is directed to an eye such that light reflected by the eyemay be captured by the imaging system. For example, eye-tracking unit130 may include a coherent light source (e.g., a laser diode) emittinglight in the visible spectrum or infrared spectrum, and a cameracapturing the light reflected by the user's eye. As another example,eye-tracking unit 130 may capture reflected radio waves emitted by aminiature radar unit. Eye-tracking unit 130 may use low-power lightemitters that emit light at frequencies and intensities that would notinjure the eye or cause physical discomfort. Eye-tracking unit 130 maybe arranged to increase contrast in images of an eye captured byeye-tracking unit 130 while reducing the overall power consumed byeye-tracking unit 130 (e.g., reducing power consumed by a light emitterand an imaging system included in eye-tracking unit 130). For example,in some implementations, eye-tracking unit 130 may consume less than 100milliwatts of power.

Near-eye display 120 may use the orientation of the eye to, e.g.,determine an inter-pupillary distance (IPD) of the user, determine gazedirection, introduce depth cues (e.g., blur image outside of the user'smain line of sight), collect heuristics on the user interaction in theVR media (e.g., time spent on any particular subject, object, or frameas a function of exposed stimuli), some other functions that are basedin part on the orientation of at least one of the user's eyes, or somecombination thereof. Because the orientation may be determined for botheyes of the user, eye-tracking unit 130 may be able to determine wherethe user is looking. For example, determining a direction of a user'sgaze may include determining a point of convergence based on thedetermined orientations of the user's left and right eyes. A point ofconvergence may be the point where the two foveal axes of the user'seyes intersect. The direction of the user's gaze may be the direction ofa line passing through the point of convergence and the mid-pointbetween the pupils of the user's eyes.

Input/output interface 140 may be a device that allows a user to sendaction requests to console 110. An action request may be a request toperform a particular action. For example, an action request may be tostart or to end an application or to perform a particular action withinthe application. Input/output interface 140 may include one or moreinput devices. Example input devices may include a keyboard, a mouse, agame controller, a glove, a button, a touch screen, or any othersuitable device for receiving action requests and communicating thereceived action requests to console 110. An action request received bythe input/output interface 140 may be communicated to console 110, whichmay perform an action corresponding to the requested action. In someembodiments, input/output interface 140 may provide haptic feedback tothe user in accordance with instructions received from console 110. Forexample, input/output interface 140 may provide haptic feedback when anaction request is received, or when console 110 has performed arequested action and communicates instructions to input/output interface140.

Console 110 may provide content to near-eye display 120 for presentationto the user in accordance with information received from one or more ofexternal imaging device 150, near-eye display 120, and input/outputinterface 140. In the example shown in FIG. 1, console 110 may includean application store 112, a headset tracking module 114, an artificialreality engine 116, and eye-tracking module 118. Some embodiments ofconsole 110 may include different or additional modules than thosedescribed in conjunction with FIG. 1. Functions further described belowmay be distributed among components of console 110 in a different mannerthan is described here.

In some embodiments, console 110 may include a processor and anon-transitory computer-readable storage medium storing instructionsexecutable by the processor. The processor may include multipleprocessing units executing instructions in parallel. Thecomputer-readable storage medium may be any memory, such as a hard diskdrive, a removable memory, or a solid-state drive (e.g., flash memory ordynamic random access memory (DRAM)). In various embodiments, themodules of console 110 described in conjunction with FIG. 1 may beencoded as instructions in the non-transitory computer-readable storagemedium that, when executed by the processor, cause the processor toperform the functions further described below.

Application store 112 may store one or more applications for executionby console 110. An application may include a group of instructions that,when executed by a processor, generates content for presentation to theuser. Content generated by an application may be in response to inputsreceived from the user via movement of the user's eyes or inputsreceived from the input/output interface 140. Examples of theapplications may include gaming applications, conferencing applications,video playback application, or other suitable applications.

Headset tracking module 114 may track movements of near-eye display 120using slow calibration information from external imaging device 150. Forexample, headset tracking module 114 may determine positions of areference point of near-eye display 120 using observed locators from theslow calibration information and a model of near-eye display 120.Headset tracking module 114 may also determine positions of a referencepoint of near-eye display 120 using position information from the fastcalibration information. Additionally, in some embodiments, headsettracking module 114 may use portions of the fast calibrationinformation, the slow calibration information, or some combinationthereof, to predict a future location of near-eye display 120. Headsettracking module 114 may provide the estimated or predicted futureposition of near-eye display 120 to artificial reality engine 116.

Headset tracking module 114 may calibrate the artificial reality systemenvironment 100 using one or more calibration parameters, and may adjustone or more calibration parameters to reduce errors in determining theposition of near-eye display 120. For example, headset tracking module114 may adjust the focus of external imaging device 150 to obtain a moreaccurate position for observed locators on near-eye display 120.Moreover, calibration performed by headset tracking module 114 may alsoaccount for information received from IMU 132. Additionally, if trackingof near-eye display 120 is lost (e.g., external imaging device 150 losesline of sight of at least a threshold number of locators 126), headsettracking module 114 may re-calibrate some or all of the calibrationparameters.

Artificial reality engine 116 may execute applications within artificialreality system environment 100 and receive position information ofnear-eye display 120, acceleration information of near-eye display 120,velocity information of near-eye display 120, predicted future positionsof near-eye display 120, or some combination thereof from headsettracking module 114. Artificial reality engine 116 may also receiveestimated eye position and orientation information from eye-trackingmodule 118. Based on the received information, artificial reality engine116 may determine content to provide to near-eye display 120 forpresentation to the user. For example, if the received informationindicates that the user has looked to the left, artificial realityengine 116 may generate content for near-eye display 120 that mirrorsthe user's eye movement in a virtual environment. Additionally,artificial reality engine 116 may perform an action within anapplication executing on console 110 in response to an action requestreceived from input/output interface 140, and provide feedback to theuser indicating that the action has been performed. The feedback may bevisual or audible feedback via near-eye display 120 or haptic feedbackvia input/output interface 140.

Eye-tracking module 118 may receive eye-tracking data from eye-trackingunit 130 and determine the position of the user's eye based on the eyetracking data. The position of the eye may include an eye's orientation,location, or both relative to near-eye display 120 or any elementthereof. Because the eye's axes of rotation change as a function of theeye's location in its socket, determining the eye's location in itssocket may allow eye-tracking module 118 to more accurately determinethe eye's orientation.

In some embodiments, eye-tracking module 118 may store a mapping betweenimages captured by eye-tracking unit 130 and eye positions to determinea reference eye position from an image captured by eye-tracking unit130. Alternatively or additionally, eye-tracking module 118 maydetermine an updated eye position relative to a reference eye positionby comparing an image from which the reference eye position isdetermined to an image from which the updated eye position is to bedetermined. Eye-tracking module 118 may determine eye position usingmeasurements from different imaging devices or other sensors. Forexample, eye-tracking module 118 may use measurements from a sloweye-tracking system to determine a reference eye position, and thendetermine updated positions relative to the reference eye position froma fast eye-tracking system until a next reference eye position isdetermined based on measurements from the slow eye-tracking system.

Eye-tracking module 118 may also determine eye calibration parameters toimprove precision and accuracy of eye tracking. Eye calibrationparameters may include parameters that may change whenever a user donsor adjusts near-eye display 120. Example eye calibration parameters mayinclude an estimated distance between a component of eye-tracking unit130 and one or more parts of the eye, such as the eye's center, pupil,cornea boundary, or a point on the surface of the eye. Other example eyecalibration parameters may be specific to a particular user and mayinclude an estimated average eye radius, an average corneal radius, anaverage sclera radius, a map of features on the eye surface, and anestimated eye surface contour. In embodiments where light from theoutside of near-eye display 120 may reach the eye (as in some augmentedreality applications), the calibration parameters may include correctionfactors for intensity and color balance due to variations in light fromthe outside of near-eye display 120. Eye-tracking module 118 may use eyecalibration parameters to determine whether the measurements captured byeye-tracking unit 130 would allow eye-tracking module 118 to determinean accurate eye position (also referred to herein as “validmeasurements”). Invalid measurements, from which eye-tracking module 118may not be able to determine an accurate eye position, may be caused bythe user blinking, adjusting the headset, or removing the headset,and/or may be caused by near-eye display 120 experiencing greater than athreshold change in illumination due to external light. In someembodiments, at least some of the functions of eye-tracking module 118may be performed by eye-tracking unit 130.

FIG. 2 is a perspective view of an example of a near-eye display in theform of a head-mounted display (HMD) device 200 for implementing some ofthe examples disclosed herein. HMD device 200 may be a part of, e.g., avirtual reality (VR) system, an augmented reality (AR) system, a mixedreality (MR) system, or some combinations thereof. HMD device 200 mayinclude a body 220 and a head strap 230. FIG. 2 shows a top side 223, afront side 225, and a right side 227 of body 220 in the perspectiveview. Head strap 230 may have an adjustable or extendible length. Theremay be a sufficient space between body 220 and head strap 230 of HMDdevice 200 for allowing a user to mount HMD device 200 onto the user'shead. In various embodiments, HMD device 200 may include additional,fewer, or different components. For example, in some embodiments, HMDdevice 200 may include eyeglass temples and temples tips as shown in,for example, FIG. 2, rather than head strap 230.

HMD device 200 may present to a user media including virtual and/oraugmented views of a physical, real-world environment withcomputer-generated elements. Examples of the media presented by HMDdevice 200 may include images (e.g., two-dimensional (2D) orthree-dimensional (3D) images), videos (e.g., 2D or 3D videos), audios,or some combinations thereof. The images and videos may be presented toeach eye of the user by one or more display assemblies (not shown inFIG. 2) enclosed in body 220 of HMD device 200. In various embodiments,the one or more display assemblies may include a single electronicdisplay panel or multiple electronic display panels (e.g., one displaypanel for each eye of the user). Examples of the electronic displaypanel(s) may include, for example, a liquid crystal display (LCD), anorganic light emitting diode (OLED) display, an inorganic light emittingdiode (ILED) display, a micro light emitting diode (mLED) display, anactive-matrix organic light emitting diode (AMOLED) display, atransparent organic light emitting diode (TOLED) display, some otherdisplay, or some combinations thereof. HMD device 200 may include twoeye box regions.

In some implementations, HMD device 200 may include various sensors (notshown), such as depth sensors, motion sensors, position sensors, and eyetracking sensors. Some of these sensors may use a structured lightpattern for sensing. In some implementations, HMD device 200 may includean input/output interface for communicating with a console. In someimplementations, HMD device 200 may include a virtual reality engine(not shown) that can execute applications within HMD device 200 andreceive depth information, position information, accelerationinformation, velocity information, predicted future positions, or somecombination thereof of HMD device 200 from the various sensors. In someimplementations, the information received by the virtual reality enginemay be used for producing a signal (e.g., display instructions) to theone or more display assemblies. In some implementations, HMD device 200may include locators (not shown, such as locators 126) located in fixedpositions on body 220 relative to one another and relative to areference point. Each of the locators may emit light that is detectableby an external imaging device.

FIG. 3 is a perspective view of a simplified example near-eye display300 in the form of a pair of glasses for implementing some of theexamples disclosed herein. Near-eye display 300 may be a specificimplementation of near-eye display 120 of FIG. 1, and may be configuredto operate as a virtual reality display, an augmented reality display,and/or a mixed reality display. Near-eye display 300 may include a frame305 and a display 310. Display 310 may be configured to present contentto a user. In some embodiments, display 310 may include displayelectronics and/or display optics. For example, as described above withrespect to near-eye display 120 of FIG. 1, display 310 may include anLCD display panel, an LED display panel, or an optical display panel(e.g., a waveguide display assembly).

Near-eye display 300 may further include various sensors 350 a, 350 b,350 c, 350 d, and 350 e on or within frame 305. In some embodiments,sensors 350 a-350 e may include one or more depth sensors, motionsensors, position sensors, inertial sensors, or ambient light sensors.In some embodiments, sensors 350 a-350 e may include one or more imagesensors configured to generate image data representing different fieldsof views in different directions. In some embodiments, sensors 350 a-350e may be used as input devices to control or influence the displayedcontent of near-eye display 300, and/or to provide an interactiveVR/AR/MR experience to a user of near-eye display 300. In someembodiments, sensors 350 a-350 e may also be used for stereoscopicimaging.

In some embodiments, near-eye display 300 may further include one ormore illuminators 330 to project light into the physical environment.The projected light may be associated with different frequency bands(e.g., visible light, infra-red light, ultra-violet light, etc.), andmay serve various purposes. For example, illuminator(s) 330 may projectlight in a dark environment (or in an environment with low intensity ofinfra-red light, ultra-violet light, etc.) to assist sensors 350 a-350 ein capturing images of different objects within the dark environment. Insome embodiments, illuminator(s) 330 may be used to project certainlight pattern onto the objects within the environment. In someembodiments, illuminator(s) 330 may be used as locators, such aslocators 126 described above with respect to FIG. 1.

In some embodiments, near-eye display 300 may also include ahigh-resolution camera 340. Camera 340 may capture images of thephysical environment in the field of view. The captured images may beprocessed, for example, by a virtual reality engine (e.g., artificialreality engine 116 of FIG. 1) to add virtual objects to the capturedimages or modify physical objects in the captured images, and theprocessed images may be displayed to the user by display 310 for AR orMR applications.

FIG. 4 illustrates an example of an optical see-through augmentedreality system 400 using a waveguide display according to certainembodiments. Augmented reality system 400 may include a projector 410and a combiner 415. Projector 410 may include a light source or imagesource 412 and projector optics 414. In some embodiments, image source412 may include a plurality of pixels that displays virtual objects,such as an LCD display panel or an LED display panel. In someembodiments, image source 412 may include a light source that generatescoherent or partially coherent light. For example, image source 412 mayinclude a laser diode, a vertical cavity surface emitting laser, and/ora light emitting diode. In some embodiments, image source 412 mayinclude a plurality of light sources each emitting a monochromatic imagelight corresponding to a primary color (e.g., red, green, or blue). Insome embodiments, image source 412 may include an optical patterngenerator, such as a spatial light modulator. Projector optics 414 mayinclude one or more optical components that can condition the light fromimage source 412, such as expanding, collimating, scanning, orprojecting light from image source 412 to combiner 415. The one or moreoptical components may include, for example, one or more lenses, liquidlenses, mirrors, apertures, and/or gratings. In some embodiments,projector optics 414 may include a liquid lens (e.g., a liquid crystallens) with a plurality of electrodes that allows scanning of the lightfrom image source 412.

Combiner 415 may include an input coupler 430 for coupling light fromprojector 410 into a substrate 420 of combiner 415. Input coupler 430may include a volume holographic grating, a diffractive optical elements(DOE) (e.g., a surface-relief grating), or a refractive coupler (e.g., awedge or a prism). Input coupler 430 may have a coupling efficiency ofgreater than 30%, 50%, 75%, 90%, or higher for visible light. As usedherein, visible light may refer to light with a wavelength between about380 nm to about 750 nm. Light coupled into substrate 420 may propagatewithin substrate 420 through, for example, total internal reflection(TIR). Substrate 420 may be in the form of a lens of a pair ofeyeglasses. Substrate 420 may have a flat or a curved surface, and mayinclude one or more types of dielectric materials, such as glass,quartz, plastic, polymer, poly(methyl methacrylate) (PMMA), crystal, orceramic. A thickness of the substrate may range from, for example, lessthan about 1 mm to about 10 mm or more. Substrate 420 may be transparentto visible light. A material may be “transparent” to a light beam if thelight beam can pass through the material with a high transmission rate,such as larger than 50%, 40%, 75%, 80%, 90%, 95%, or higher, where asmall portion of the light beam (e.g., less than 50%, 40%, 25%, 20%,10%, 5%, or less) may be scattered, reflected, or absorbed by thematerial. The transmission rate (i.e., transmissivity) may berepresented by either a photopically weighted or an unweighted averagetransmission rate over a range of wavelengths, or the lowesttransmission rate over a range of wavelengths, such as the visiblewavelength range.

Substrate 420 may include or may be coupled to a plurality of outputcouplers 440 configured to extract at least a portion of the lightguided by and propagating within substrate 420 from substrate 420, anddirect extracted light 460 to an eye 490 of the user of augmentedreality system 400. As input coupler 430, output couplers 440 mayinclude grating couplers (e.g., volume holographic gratings orsurface-relief gratings), other DOEs, prisms, etc. Output couplers 440may have different coupling (e.g., diffraction) efficiencies atdifferent locations. Substrate 420 may also allow light 450 fromenvironment in front of combiner 415 to pass through with little or noloss. Output couplers 440 may also allow light 450 to pass through withlittle loss. For example, in some implementations, output couplers 440may have a low diffraction efficiency for light 450 such that light 450may be refracted or otherwise pass through output couplers 440 withlittle loss, and thus may have a higher intensity than extracted light460. In some implementations, output couplers 440 may have a highdiffraction efficiency for light 450 and may diffract light 450 tocertain desired directions (i.e., diffraction angles) with little loss.As a result, the user may be able to view combined images of theenvironment in front of combiner 415 and virtual objects projected byprojector 410.

FIG. 5 is a cross-sectional view of an example of a near-eye display 500according to certain embodiments. Near-eye display 500 may include atleast one display assembly 510. Display assembly 510 may be configuredto direct image light (i.e., display light) to an eyebox located at exitpupil 530 and to user's eye 520. It is noted that, even though FIG. 5and other figures in the present disclosure show an eye of a user of anear-eye display for illustration purposes, the eye of the user is not apart of the corresponding near-eye display.

As HMD device 200 and near-eye display 300, near-eye display 500 mayinclude a frame 505 and a display assembly 510 that includes a display512 and/or display optics 514 coupled to or embedded in frame 505. Asdescribed above, display 512 may display images to the user electrically(e.g., using LCD) or optically (e.g., using an waveguide display andoptical couplers) according to data received from a console, such asconsole 110. Display 512 may include sub-pixels to emit light of apredominant color, such as red, green, blue, white, or yellow. In someembodiments, display assembly 510 may include a stack of one or morewaveguide displays including, but not restricted to, a stacked waveguidedisplay, a varifocal waveguide display, etc. The stacked waveguidedisplay is a polychromatic display (e.g., a red-green-blue (RGB)display) created by stacking waveguide displays whose respectivemonochromatic sources are of different colors. The stacked waveguidedisplay may also be a polychromatic display that can be projected onmultiple planes (e.g. multi-planar colored display). In someconfigurations, the stacked waveguide display may be a monochromaticdisplay that can be projected on multiple planes (e.g. multi-planarmonochromatic display). The varifocal waveguide display is a displaythat can adjust a focal position of image light emitted from thewaveguide display. In alternate embodiments, display assembly 510 mayinclude the stacked waveguide display and the varifocal waveguidedisplay.

Display optics 514 may be similar to display optics 124 and may displayimage content optically (e.g., using optical waveguides and opticalcouplers), correct optical errors associated with the image light,combine images of virtual objects and real objects, and present thecorrected image light to exit pupil 530 of near-eye display 500, wherethe user's eye 520 may be located at. Display optics 514 may also relaythe image to create virtual images that appear to be away from the imagesource and further than just a few centimeters away from the eyes of theuser. For example, display optics 514 may collimate the image source tocreate a virtual image that may appear to be far away and convertspatial information of the displayed virtual objects into angularinformation. Display optics 514 may also magnify the image source tomake the image appear larger than the actual size of the image source.More detail of the display optics is described below.

II. Display Optics

In various implementations, the optical system of a near-eye display,such as an HMD, may be pupil-forming or non-pupil-forming.Non-pupil-forming HMDs may not use intermediary optics to relay thedisplayed image, and thus the user's pupils may serve as the pupils ofthe HMD. Such non-pupil-forming displays may be variations of amagnifier (sometimes referred to as “simple eyepiece”), which maymagnify a displayed image to form a virtual image at a greater distancefrom the eye. The non-pupil-forming display may use fewer opticalelements. Pupil-forming HMDs may use optics similar to, for example,optics of a compound microscope or telescope, and may include aninternal aperture and some forms of projection optics that magnify anintermediary image and relay it to the exit pupil. The more complexoptical system of the pupil-forming HMDs may allow for a larger numberof optical elements in the path from the image source to the exit-pupil,which may be used to correct optical aberrations and generate focalcues, and may provide design freedom for packaging the HMD. For example,a number of reflectors (e.g., mirrors) may be inserted in the opticalpath so that the optical system may be folded or wrapped around to fitin a compact HMD.

FIG. 6 illustrates an example of an optical system 600 with anon-pupil-forming configuration for a near-eye display device accordingto certain embodiments. Optical system 600 may include projector optics610 and an image source 620. Projector optics 610 may function as amagnifier. FIG. 6 shows that image source 620 is in front of projectoroptics 610. In some other embodiments, image source 620 may be locatedoutside of the field of view of a user's eye 690. For example, one ormore reflectors or directional couplers as shown in, for example, FIG.4, may be used to reflect light from an image source to make the imagesource appear to be at the location of image source 620 shown in FIG. 6.Thus, image source 620 may be similar to image source 412 describedabove. Light from an area (e.g., a pixel or a light emitting source) onimage source 620 may be directed to user's eye 690 by projector optics610. Light directed by projector optics 610 may form virtual images onan image plane 630. The location of image plane 630 may be determinedbased on the location of image source 620 and the focal length ofprojector optics 610. User's eye 690 may form a real image on the retinaof user's eye 690 using light directed by projector optics 610. In thisway, objects at different spatial locations on image source 620 mayappear to be objects on an image plane far away from user's eye 690 atdifferent viewing angles.

FIG. 7 illustrates an example of an optical system 700 with a pupilforming configuration for a near-eye display device according to certainembodiments. Optical system 700 may include an image source 710, a firstrelay lens 720, and a second relay lens 730. Even though image source710, first relay lens 720, and second relay lens 730 are shown as infront of a user's eye 790, one or more of them may be physically locatedoutside of the field of view of user's eye 790 when, for example, one ormore reflectors or directional couplers are used to change thepropagation direction of the light. Image source 710 may be similar toimage source 412 described above. First relay lens 720 may include oneor more lenses, and may produce an intermediate image 750 of imagesource 710. Second relay lens 730 may include one or more lenses, andmay relay intermediate image 750 to an exit pupil 740. As shown in FIG.7, objects at different spatial locations on image source 710 may appearto be objects far away from the user's eye 790 at different viewingangles. The light from different angles may then be focused by the eyeonto different locations on retina 792 of user's eye 790. For example,at least some portion of the light may be focused on fovea 794 on retina792.

Optical system 600 and optical system 700 may be large and heavy ifimplemented using conventional optics. In some implementations, foldedoptics including reflective optical elements may be used to implementcompact HMD systems with a large field of view.

III. Folded Lens

FIG. 8 shows an embodiment of a folded-lens system 800 comprising afirst lens M-1 (or a curved substrate) and a second lens M-2 (or acurved substrate). Light from a display 804 may be relayed to an eye box808 by folded-lens system 800. First lens M-1 may include a partialreflector 812 formed on it. Partial reflector 812 may have atransmissivity T that is equal to or greater than 20% or 40% and equalto or less than 60% or 90% (e.g., a 50/50 mirror with T=50% +/−2, 5, or10%). Second lens M-2 may include a reflective polarizer 816 formed onit. Folded-lens system 800 may also include a quarter-wave plate (notshown in FIG. 8) between first lens M-1 and second lens M-2. As shown inFIG. 8, light emitted from display 804 may be transmitted by partialreflector 812 (e.g., half of the light may be transmitted throughpartial reflector 812) and first lens M-1, reflected off reflectivepolarizer 816 on second lens M-2, reflected off partial reflector 812and first mirror M-1, and then transmitted through reflective polarizer816 to eye box 808. In this way, light may be folded within the cavityformed by partial reflector 812 and reflective polarizer 816 to increasethe effective optical path and achieve a desired optical power with acompact form factor.

FIG. 9 illustrates an embodiment a folded-lens system 900. Folded-lenssystem 900 may be a specific implementation of folded-lens system 800.Even though the components of folded-lens system 900 are shown as flatcomponents in FIG. 9, at least some of the components may have a curvedshape. For example, at least some of the components may be formed on acurved surface, such as a surface of a lens or a curved substrate asshown in, for example, FIG. 8.

In the example shown in FIG. 9, light from a display 902 travels alongan optical path (OP) 904 to an eye box 916. Light from display 902 mayfirst be converted to circularly polarized light. There may be severalways to generate circularly polarized light. One way is to use aquarter-wave plate after a linear polarizer, where the transmission axisof the linear polarizer is half way (45°) between the fast and slow axesof the quarter-wave plate. The unpolarized light can be linearlypolarized by the linear polarizer, and the linearly polarized light canbe transformed into circularly polarized light by the quarter waveplate. For example, as shown in FIG. 9, light at a first portion OP-1 ofoptical path 904 is linearly polarized after transmitting from display902 through a linear polarizer 906 (e.g., an absorptive polarizer or abeam-splitting polarizer). For example, the light may be polarized at 45degrees with respect to the x axis in an x/y plane, wherein the z axisis a direction of light propagation. The linearly polarized light maypass through a quarter-wave plate (QWP) 908 and become circularlypolarized along a second portion OP-2 of optical path 904. Morespecifically, a fast axis of QWP 908 may be aligned along they axis, andthe light may become left-handed circularly polarized after passingthrough QWP 908.

The left-handed circularly polarized light may then pass through apartial reflector 910. After passing through the partial reflector 910,the polarization of the light does not change along a third portion OP-3of optical path 904. After passing through an optical retarder 912, thelight is changed back to linearly-polarized light (e.g., at 45 degreeswith respect to the x axis) on a fourth portion OP-4 of optical path904. For example, optical retarder 912 may be a second quarter-waveplate with axes rotated by 90 degrees from the axes of QWP 908.

Light from the fourth portion OP-4 of optical path 904 may be reflectedoff a reflective linear polarizer 914 that passes light linearlypolarized at 135 degrees and reflects light linearly polarized at 45degrees. After reflected by reflective linear polarizer 914, light fromthe fourth portion OP-4 of optical path 904 may become linearlypolarized at 135 degrees at a fifth portion OP-5 of optical path 904because the electric field at the reflection surface remains unchangedin the x/y plane yet the direction of beam propagation is flipped. Lightreflected from reflective linear polarizer 914 may then pass throughoptical retarder 912 a second time and become circularly polarized(e.g., left handed) at a sixth portion OP-6 of optical path 904.

Light from the sixth portion OP-6 of optical path 904 is reflected(e.g., 50% reflected) and becomes oppositely (e.g., right-handed)circularly polarized at a seventh portion OP-7 of optical path 904.After passing through optical retarder 912 a third time, the lightbecomes linearly polarized at an eighth portion OP-8 of the optical path904, with a polarization direction (e.g., at 135 degrees) orthogonal tothe polarization direction (e.g., at 45 degrees) of the light at thefourth portion OP-4 of optical path 904. Light from the eighth portionOP-8 of optical path 904 is then transmitted through reflective linearpolarizer 914 to eye box 916. Due to the double-reflection andtriple-pass in the cavity between partial reflector 910 (e.g., on firstlens M-1) and reflective linear polarizer 914 (e.g., on second lensM-2), the total physical length of the system can be reduced.

As shown in FIG. 9, the folded optics may use one or more polarizers andone or more wave plates to transmit and reflect light of certainpolarization states within the folded optics so as to effectively “fold”the optical path. The folded optics may reduce the thickness and/orweight of the HMD, and may provide a wide field of view. However, thequality of the image displayed to a user's eye may be compromised (e.g.,due to strong ghost images) if the polarizers and/or the wave plates arenot precisely aligned. For example, linear polarizer 906 and QWP 908 mayneed to be aligned such that the polarization direction of linearpolarizer 906 is half way (45 degrees) between the fast and slow axes ofQWP 908 to generate circularly polarized light. QWP 908 and opticalretarder 912 may need to be aligned such that the fast and slow axes ofQWP 908 are aligned with the slow and fast axes of optical retarder 912,respectively, in order to make the light passing through opticalretarder 912 on OP-4 linearly polarized. Otherwise, light passingthrough optical retarder 912 on OP-4 may not be linearly polarized, andat least a portion of the light may be transmitted through reflectivelinear polarizer 914 (instead of being fully reflected) to cause ghostimages. Similarly, reflective linear polarizer 914 and optical retarder912 may need to be aligned such that the polarization direction ofreflective linear polarizer 914 is half way (45 degrees) between thefast and slow axes of optical retarder 912. In many cases, it may bedifficult, costly, or time-consuming to properly align the opticalcomponents, which may also become misaligned during use even if they areprecisely aligned initially. Thus, it is desirable to eliminate at leastsome of these optical components that may need precise alignments.

IV. Reflective Circular Polarizer

According to certain embodiments, a reflective circular polarizer may beused in the folded optics to replace a reflective linear polarizer and awave plate that may need to be aligned, thus avoiding the alignmentprocedures. The reflective circular polarizer may be configured toreflect light of a first circular polarization state while keeping thehandedness of the reflected light same as that of the incident light,and transmit light of a second (e.g., opposite) circular polarizationstate. In some embodiments, display light from a display device can bepolarized to the first circular polarization state, and then passthrough a partial reflector (e.g., a 50/50 mirror) and be reflected bythe reflective circular polarizer back to the partial reflector. Thepartial reflector may reflect the light of the first circularpolarization state into light of the second circular polarization stateback to the reflective circular polarizer. The reflective circularpolarizer may then let the light of the second circular polarizationstate reflected from the partial reflector to pass through. In this way,display light of the first circular polarization state from the displaydevice may be folded by the optical system before reaching the user'seye as light of the second polarization state. In some implementations,linear polarizer 906 and QWP 908, which in combination circularlypolarize the display light from the display device, may be replaced witha circular polarizer to further reduce the alignment requirements.

There may be many different ways to implement the reflective circularpolarizer. In some embodiments, the reflective circular polarizer may beimplemented using cholesteric liquid crystal (CLC) (also referred to aschiral liquid crystal). The polarization state of the light beingreflected by the CLC circular polarizer may depend on the handedness ofthe cholesteric helical superstructure formed by the liquid crystalmolecules. Multiple layers of cholesteric liquid crystal materials maybe used to improve the reflectivity of the reflective circularpolarizer. In some embodiments, multiple layers of cholesteric liquidcrystal with different pitches (or periods) may be used to reflect lightof different wavelengths. More details of the cholesteric liquidcrystal-based reflective circular polarizer are described below.

In liquid crystal, the rod-like liquid crystal molecules are generallyoriented with their moments of inertia roughly aligned along an axiscalled the director. Because of the anisotropic orientation of theliquid crystal molecules, physical properties of liquid crystals, suchas the refractive index, elastic constant, viscosity, dielectricconstant, thermal and electrical conductivity, etc., may also beanisotropic. Liquid crystals can also be made chiral. For example, anachiral LC host material may form a helical supra-molecular architectureif doped with a chiral material (often referred to as a chiral dopant).The liquid crystal molecules in the chiral liquid crystal may be tiltedby a finite angle with respect to the layer normal in a layeredstructure. The chirality may induce a finite azimuthal twist from onelayer to the next, producing a spiral twisting of the molecular axisalong the layer normal direction. The distance over which the LCmolecules undergo a full 360° twist is referred to as the chiral pitchp. The structure of the chiral liquid crystal repeats every half-pitchbecause the directors at 0° and ±180° are equivalent. The pitch p can bechanged when the temperature is altered or when other molecules (e.g.,the chiral dopant) are added to the liquid crystal host. Thus, the pitchcan be tuned by doping the liquid crystal host with different materialsor different concentrations of a material, such as the chiral dopant. Insome liquid crystal devices, the pitch may be on the same order as thewavelength of visible light. Such CLC devices may exhibit unique opticalproperties, such as Bragg reflection and low-threshold laser emission.Furthermore, CLCs also present special electro-optic effects, forexample, memory effect, grating effect, as well as the withdrawal effectof spiral.

Another structural parameter of the cholesteric liquid crystals is thetwist sense, which determines the handedness of a helix (left- orright-handed). Due to the unique helical structures, cholesteric liquidcrystals may exhibit particular optical properties, such ascharacteristics of selective light reflection, optical rotation effect,and circular dichroism, which distinguish them from the other liquidcrystal materials. From the macroscopic perspective, the handednessdetermines the optical reflective characteristics of cholesteric liquidcrystals. CLC molecules may form a spiral in space along the z-directionaccording to:

${{n(r)} = \begin{Bmatrix}{\cos( {{\frac{2\pi}{p}z} + \varphi_{0}} )} \\{\sin( {{\frac{2\pi}{p}z} + \varphi_{0}} )} \\0\end{Bmatrix}},$where p is the pitch of the helix and φ₀ is a constant that depends onthe boundary conditions. This helical structure may lead to thereflection of circular polarized light with the handedness unchanged.

FIG. 10 illustrates an embodiment of a cholesteric liquid crystalcircular polarizer 1000 having a left-handed helical structure. Circularpolarizer 1000 may include a plurality of layers embedded between asubstrate 1010 and a substrate 1020. Insert 1050 shows a half pitch ofthe helical structure. As shown in the insert 1050, liquid crystalmolecules 1002 in the plurality of layers may be tilted by differentangles with respect to the layer normal (the z direction) and mayproduce a spiral twisting of the molecular axis along the layer normal.In the example shown in FIG. 10, the liquid crystal molecules form aleft-handed helical structure. As such, left-handed circularly polarizedlight 1030 that is incident on circular polarizer 1000 may be reflectedback as left-handed circularly polarized light 1032. On the other hand,right-handed circularly polarized light 1040 that is incident oncircular polarizer 1000 may pass through circular polarizer 1000 asright-handed circularly polarized light 1042.

FIG. 11 illustrates an embodiment of a cholesteric liquid crystalcircular polarizer 1100 having a right-handed helical structure.Circular polarizer 1100 may include a plurality of layers 1110. Insert1150 shows a half pitch of the helical structure. As shown in insert1150, liquid crystal molecules 1102 in the plurality of layers 1110 maybe tilted by different angles with respect to the layer normal (the zdirection) and produce a spiral twisting of the molecular axis along thelayer normal. In the example shown in FIG. 11, the liquid crystalmolecules form a right-handed helical structure. As such, whenunpolarized light 1120 that includes a right-handed circularly polarizedcomponent and a left-handed circularly polarized component is incidenton circular polarizer 1100, the right-handed circularly polarizedcomponent may be reflected back as right-handed circularly polarizedlight 1130. In contrast, the left-handed circularly polarized componentmay pass through circular polarizer 1100 as left-handed circularlypolarized light 1140.

Thus, the handedness of the circularly polarized light reflected by thecircular polarizer may be selected by twisting the liquid crystalmolecules in the circular polarizer according to a correspondinghandedness. In contrast, a glass or metal reflector may reflect incidentcircularly polarized light such that the reflected circularly polarizedlight has an opposite handedness compared with the incident circularlypolarized light. Such differences in reflective properties between thereflective CLC circular polarizer and a metal or glass reflector areshown in FIGS. 12A and 12B below.

FIG. 12A illustrates an embodiment of a cholesteric liquid crystalcircular polarizer 1200 with right-handed helixes. Circular polarizer1200 includes liquid crystal molecules 1220 embedded between twosubstrates 1210. Liquid crystal molecules 1220 form a right-handedhelical structure. As such, right-handed circularly polarized light 1230incident on circular polarizer 1200 may be reflected back asright-handed circularly polarized light 1232, while left-handedcircularly polarized light 1240 incident on circular polarizer 1200 maypass through circular polarizer 1200 as left-handed circularly polarizedlight 1242.

FIG. 12B illustrates the reflection of circularly polarized light by aglass or metal mirror 1250. As illustrated, right-handed circularlypolarized light 1260 incident on glass or metal mirror 1250 may bereflected back as left-handed circularly polarized light 1270.

FIG. 13 illustrates normalized selective reflection spectra of examplecholesteric liquid crystal cells with various cell thicknesses. Due tothe periodic change of the refractive indices arising from the helicalstructure, CLCs can selectively reflect the incident light based on theBragg relationship. The central wavelength λ and the wavelength range(i.e., the bandwidth) Δλ of the selective reflection may be denoted asλ=np and Δλ=Δnp, respectively, where n=(n_(o)+n_(e))/2 is the average ofthe ordinary (n_(o)) and the extraordinary (n_(e)) refractive indices ofthe locally uniaxial structure, p is the helical pitch, andΔn=n_(e)−n_(o) is the birefringence. Within the reflection bandwidth,cholesteric liquid crystals with left-handed helical structures mayallow right-handed circularly polarized light to go through and reflectleft-handed circularly polarized light. Cholesteric liquid crystals withright-handed helical structures may allow left-handed circularlypolarized light to go through and reflect right-handed circularlypolarized light. Beyond the reflection bandwidth, both left-handed andright-handed circularly polarized light is transmitted. In addition, dueto the polarization-selectivity property of the cholesteric liquidcrystals, when an ordinary unpolarized light goes through CLCs, themaximum reflectivity is usually limited to 50%, and the other 50% ormore may be transmitted through the cholesteric liquid crystals.

In the examples shown in FIG. 13, a first cholesteric liquid crystalcell may include 6 pitches, and the reflective spectrum of the firstcholesteric liquid crystal cell is shown by curve 1310. Curve 1310 showsthat the maximum normalized reflectivity of the first cholesteric liquidcrystal cell in the visible light band is about 80% and the wavelengthselectivity is not very good. A second cholesteric liquid crystal cellmay include 10 pitches. The reflective spectrum of the secondcholesteric liquid crystal cell is shown by curve 1320. Curve 1320 showsthat the maximum normalized reflectivity of the second cholestericliquid crystal cell in the visible light band is close to 95% and thewavelength selectivity is much better than the first cholesteric liquidcrystal cell. Curves 1330 and 1340 show the reflective spectra of athird and fourth cholesteric liquid crystal cells that have a cellthickness of 15 and 20 pitches, respectively. As illustrated, the thirdand fourth cholesteric liquid crystal cells have a peak normalizedreflectivity close to 100% and have a very good wavelength selectivity.Thus, light of one circular polarization state (e.g., right-handed orleft-handed) may be almost all reflected, and thus the transmitted lightmay only include light of the opposite circular polarization state(e.g., left-handed or right-handed).

A cholesteric liquid crystal-based circular polarizer may be fabricatedin various ways on a substrate, such as a transparent glass substrate.For example, the cholesteric liquid crystal-based circular polarizer maybe formed using double twist cholesteric liquid crystal layers (wherethe liquid crystal molecules may twist along two directions, oneperpendicular to the substrate and the other one parallel to thesubstrate) or liquid crystal polymer layers. In one embodiment, analignment layer including a desired pattern may be formed on thesubstrate using, for example, photolithography, direct write (e.g.,using e-beam), or holographic recording. A liquid crystal polymer thinfilm may be coated on the alignment layer. The liquid crystal polymer(or monomer) molecules may align according to the pattern on thealignment layer. A UV polymerization (or curing) process may be used topolymerize the liquid crystal polymer (or monomer) molecules, which maycause the liquid crystal molecules to be aligned to be parallel orperpendicular to incident linearly polarized UV light, and fix theliquid crystal molecules in the thin film. The coating andpolymerization processes may be performed repeatedly to create thethree-dimensional spiral structure of liquid crystal polymer moleculeswith a desired thickness (or number of pitches) in order to achieve adesired reflectivity.

V. Folded-Lens Using Circular Polarizer

The folded-lens system 800 or 900 may be simplified and improved usingthe CLC circular polarizers described above with respect to FIGS. 10-12.For example, a CLC circular polarizer can be used to replace linearpolarizer 906 and QWP 908, or replace optical retarder 912 andreflective linear polarizer 914. Thus, the alignment between opticalretarder 912 and reflective linear polarizer 914 may be eliminatedbecause they are replaced by a single reflective circular polarizer. Thealignment between linear polarizer 906 and QWP 908 may be eliminated ifthey are replaced by a single circular polarizer (e.g., a reflective orabsorptive circular polarizer). The alignment between QWP 908 andreflective linear polarizer 914 (and optical retarder 912) can also beeliminated because the light transmitted or reflected by the circularpolarizer is either left-handed circularly polarized light orright-handed circularly polarized light, rather than linearly polarizedalong a certain direction or angle.

FIG. 14 illustrates an example of a folded-lens system 1400 includingone or more circular polarizers according to certain embodiments.Folded-lens system 1400 may be used together with a display 1402. Lightfrom display 1402 may travel through folded-lens system 1400 along anoptical path (OP) 1404 to a user's eye. In a first portion OP-1 ofoptical path 1404, light from display 1402 may be unpolarized. Theunpolarized light from display 1402 may first be converted to circularlypolarized light by a circular polarizer 1408. In the example shown inFIG. 14, after passing through circular polarizer 1408, light fromdisplay 1402 becomes left-handed circularly polarized along a secondportion OP-2 of optical path 1404.

After passing through a partial reflector 1410, the polarization stateof the light does not change along a third portion OP-3 of optical path1404. Light from third portion OP-3 of optical path 1404 may reach areflective polarizer 1414, which may be a reflective CLC circularpolarizer as described above. In the example shown in FIG. 14,reflective polarizer 1414 may include a left-handed circular polarizerand thus may reflective left-handed circularly polarized light whiletransmitting right-handed circularly polarized light as shown in FIG.10. Left-handed circularly polarized light reflected by reflectivepolarizer 1414 may propagate along a fourth portion OP-4 of optical path1404 before it reaches partial reflector 1410. Partial reflector 1410may reflect left-handed circularly polarized light into right-handedcircularly polarized light as described above with respect to, forexample, FIG. 9 or FIG. 12B. Right-handed circularly polarized lightreflected from partial reflector 1410 may propagate along a fifthportion OP-5 of optical path 1404 and reach reflective polarizer 1414again. As described above, in the example shown in FIG. 14, reflectivepolarizer 1414 may be a left-handed circular polarizer that transmitsright-handed circularly polarized light with little or no loss. Afterpassing through reflective polarizer 1414, the right-handed circularlypolarized light may propagate along a sixth portion OP-6 of optical path1404 towards user's eyes.

Due to the double-reflection in the cavity formed by partial reflector1410 and reflective polarizer 1414, light from display 1402 may passthrough the cavity three times, and thus a total physical length of thesystem (including the distance between partial reflector 1410 andreflective polarizer 1414) can be reduced without reducing the opticallength.

In various embodiments, any of circular polarizer 1408, partialreflector 1410, and reflective polarizer 1414 may have a flat or curvedshape. For example, any of circular polarizer 1408, partial reflector1410, and reflective polarizer 1414 may be formed on a flat or curvedsubstrate. In some embodiments, any of circular polarizer 1408, partialreflector 1410, and reflective polarizer 1414 may be formed on a surfaceof a lens (e.g., a concave or convex lens) as described above withrespect to FIG. 8.

VI. Folded-Lens for Display Mode and See-Through Mode

In some applications, it may be desirable that a near-eye display systemcan be used in both (1) a display mode (e.g., in VR or AR applications)where images from an near-eye display device (e.g., various LCD or LEDdisplays) can be projected to the user's eyes, and (2) an opticalsee-through mode where ambient light can pass through the near-eyedisplay system to the user's eyes. This may be achieved by using foldedoptics that (1) fold light of a first polarization state (e.g., acircularly polarized light, such as left-handed circularly polarizedlight) from the display device, and (2) transmit (without folding) lightof a second polarization state (e.g., another circularly polarizedlight, such as right-handed circularly polarized light) for thesee-through mode, thus producing different optical powers for thedisplay mode (e.g., a large optical power) and see-through mode (e.g., asmall or close to zero optical power).

Folded-lens system 1400 described above may also be used in thesee-through mode where no displayed image is projected. As shown in FIG.14, in the see-through mode, circular polarizer 1408 and/or display 1402(if not transparent) can be removed. The right-handed circularlypolarized light from the ambient environment may pass through atransparent display (e.g., display 1402), partial reflector 1410, andreflective polarizer 1414 along an optical path 1418, and reach theuser's eyes. However, as described above, left-handed circularlypolarized light from the ambient environment may also pass through thetransparent display (e.g., display 1402) and partial reflector 1410, andmay be reflected by reflective polarizer 1414 back to partial reflector1410. Partial reflector 1410 may then reflect the left-handed circularlypolarized light into right-handed circularly polarized light towardsreflective polarizer 1414, which may transmit the right-handedcircularly polarized light towards the user's eye. Because theright-handed circularly polarized light passes through the cavity formedby partial reflector 1410 and reflective polarizer 1414 once, theoptical power of folded-lens system 1400 for right-handed circularlypolarized light may be relative small, for example, close to zero. Onthe other hand, the left-handed circularly polarized light may bereflected back and forth within the cavity formed by partial reflector1410 and reflective polarizer 1414, and thus the optical power offolded-lens system 1400 for left-handed circularly polarized light maybe relative large.

Thus, in the see-through mode, light of a first polarization state(e.g., left-handed circularly polarized light) and light of a secondpolarization state (e.g., right-handed circularly polarized light) froma same object may both reach user's eyes, but may be refracted and/orreflected with different optical powers. Therefore, the image of theambient environment may be blurred due to the different focusing powersexperienced by the light of the first polarization state and the lightof the second polarization state. The brightness, contrast, andsharpness of the image may thus be decreased.

As described above, the orientation of the liquid crystal molecules in aCLC reflective circular polarizer may be aligned in a certain manner toform, for example, a cholesteric helical superstructure, where thepolarization state of the light reflected by the circular polarizer maybe determined by the handedness of the cholesteric helicalsuperstructure. In many liquid crystal devices (e.g., the reflectivecircular polarizer described above), the orientation (or alignment) ofthe liquid crystal molecules can be changed or realigned by applying anvoltage signal on the liquid crystal device. For example, when a voltagesignal is applied to the liquid crystal device, the liquid crystalmolecules of the liquid crystal device may be realigned such that thedirectors of the liquid crystal molecules are parallel to the electricfield E, and thus the liquid crystal device may transmit light of anypolarization. Therefore, a circular polarizer as described above maybecome transparent for light of any polarization state when a voltagesignal is applied to the circular polarizer.

As such, the operation of a near-eye display device having a circularpolarizer as described above may be switched between the display mode(with light reflection by the reflective circular polarizer) and thesee-through mode (with no light reflection by the reflective circularpolarizer) by applying voltage signals with different levels orpolarities to the circular polarizer. For example, in some embodiments,when no voltage signal is applied to the reflective circular polarizer,display light may be polarized to a first circular polarization state(e.g., left-handed or right-handed) using a circular polarizer (e.g.,reflective, absorptive, or beam-splitting circular polarizer). Thedisplay light of the first circular polarization state may pass througha 50/50 mirror and may then be reflected back to the 50/50 mirror by aCLC reflective circular polarizer as described above with respect toFIG. 14. The 50/50 mirror may reflect the display light of the firstcircular polarization state into light of a second circular polarizationstate (e.g., right-handed or left-handed) that can be transmitted by thereflective circular polarizer. Thus, the reflective circular polarizermay help to fold the light in the display mode to project images on animage plane. When a voltage signal is applied to the reflective circularpolarizer, the liquid crystal molecules may be aligned with theelectrical field, and thus light of any polarization state can passthrough the reflective circular polarizer (which may become transparentto light of any polarization state by the voltage signal) without beingfolded. In this way, the folded-lens system described above can be usedfor both the display mode and the see-through mode, without compromisingthe quality of the image in the see-through mode.

FIG. 15A illustrates an example of a folded-lens system 1500 including areflective circular polarizer 1514 and operating in a display modeaccording to certain embodiments. Reflective circular polarizer 1514 maybe a CLC circular polarizer as described above and may be controlled bya voltage source 1518. In the display mode, reflective circularpolarizer 1514 may be disconnected from voltage source 1518 and thus mayfunction as a reflective circular polarizer as described with respectto, for example, FIGS. 10-12. Light from display 1502 (which is not apart of folded-lens system 1500) and propagating on a first portion OP-1of an optical path 1504 may be converted to circularly polarized lightby a left-handed circular polarizer 1508, and become left-handedcircularly polarized along a second portion OP-2 of optical path 1504.After passing through a partial reflector 1510 (e.g., a 50/50 mirror),the light remains left-handed circularly polarized along a third portionOP-3 of optical path 1504. Light from third portion OP-3 of optical path1504 may reach reflective circular polarizer 1514.

Reflective circular polarizer 1514 may include a left-handed circularpolarizer and thus may reflect left-handed circularly polarized lightwhile transmitting right-handed circularly polarized light. Theleft-handed circularly polarized light reflected by reflective circularpolarizer 1514 may propagate along a fourth portion OP-4 of optical path1504 before it reaches partial reflector 1510. Partial reflector 1510may reflect left-handed circularly polarized light into right-handedcircularly polarized light as described above with respect to FIG. 12B.Right-handed circularly polarized light reflected from partial reflector1510 may propagate along a fifth portion OP-5 of optical path 1504 andreach reflective circular polarizer 1514 again. Reflective circularpolarizer 1514 is a left-handed circular polarizer and thus may transmitright-handed circularly polarized light with little or no loss. Afterpassing through reflective circular polarizer 1514, the right-handedcircularly polarized light may propagate along a sixth portion OP-6 ofoptical path 1504 towards an eye box 1516. Because light from display1502 may pass through the cavity between partial reflector 1510 andreflective circular polarizer 1514 three times in the display mode, atotal physical length of the system can be reduced without reducing theoptical length, and a non-zero optical power can be achieved byfolded-lens system 1500 to project displayed images on an image plane.

FIG. 15B illustrates an example of a folded-lens system including areflective circular polarizer and operating in a see-through mode. Insome embodiments, display 1502 may be a transparent display as describedabove with respect to FIG. 4 or may be a transparent liquid crystaldisplay. In some embodiments, display 1502 may not be transparent andcan be removed or displaced in the see-through mode. In the see-throughmode, reflective circular polarizer 1514 may be connected to voltagesource 1518 and thus may become transparent to light of any polarizationstate as described above. Light from ambient environment and/or passingthrough a transparent display (e.g., display 1502) may propagate on afirst portion OP-1 of an optical path 1506, and may be converted byleft-handed circular polarizer 1508 into circularly polarized lightalong a second portion OP-2 of optical path 1506. The polarization stateof the light does not change after passing through partial reflector1510. The left-handed circularly polarized light on a third portion OP-3of optical path 1506 may reach reflective circular polarizer 1514.Because reflective circular polarizer 1514 may become transparent tolight of any polarization state when connected to voltage source 1518,it may transmit the left-handed circularly polarized light with littleor no loss towards eye box 1516. Since the light from ambientenvironment (and/or display 1502) may pass through the cavity betweenpartial reflector 1510 and reflective circular polarizer 1514 once inthe see-through mode, the physical length of the system may be similarto the optical length, and folded-lens system 1500 may have a relativelysmall optical power for ambient objects in the see-through mode. In someembodiments, folded-lens system 1500 may be configured such that theoptical power of folded-lens system 1500 can help to correct the use'svision (either near-sighted or far-sighted vision). As such, folded-lenssystem 1500 may function as a correction lens in the see-through mode.

In various embodiments, any of circular polarizer 1508, partialreflector 1510, and reflective circular polarizer 1514 may have a flator curved shape. For example, any of circular polarizer 1508, partialreflector 1510, and reflective circular polarizer 1514 may be formed ona flat or curved substrate. In some embodiments, any of circularpolarizer 1508, partial reflector 1510, and reflective circularpolarizer 1514 may be formed on a surface of a lens (e.g., a concave orconvex lens) as described above with respect to FIG. 8.

In some embodiments, display 1502 may be a transparent display, such asa transparent liquid crystal display or a waveguide display as describedabove, and folded-lens system 1500 may function as an augmented reality,mixed-reality, or hybrid reality device that can be used to presentimages of both the physical world and the virtual world to the user. Forexample, light from the physical world in front of folded-lens system1500 may pass through display 1502 and then propagate in a way similarto the display light from display 1502 to the user's eyes.

In some embodiments, folded-lens system 1500 may be formed on display1502. For example, in some embodiments, display 1502 may include anoutput surface that can transmit light from the interior of display 1502while reflecting light incident from the exterior of display 1502. Thus,partial reflector 1510 may not be needed and reflective circularpolarizer 1514 may be formed on display 1502. Light from display 1502may pass through the output surface and reach reflective circularpolarizer 1514, which would transmit light of a first circularpolarization state to user's eyes and reflect light of a second circularpolarization state back to the output surface of display 1502. Thereflected light of the second circular polarization state may bereflected by the output surface of display 1502 into light of the firstcircular polarization state back to reflective circular polarizer 1514,which would then transmit the light of the first circular polarizationstate from the output surface of display 1502 to the user's eyes.

In some embodiments, a cholesteric liquid crystal cell may include onereflection band. According to equation Δλ=Δnp=(n_(e)−n_(o))p, thebandwidth Δλ depends on the birefringence Δn and p at normal incidence.The larger the Δn and p, the larger the Δλ. For liquid crystal materialsor most colorless organic materials, Δn can be in the range of about0.03 to about 0.45 or higher. Therefore, λλ can be about 110 nm orhigher in the visible spectrum.

Cholesteric liquid crystal materials with a high Δn may be difficult tosynthesize and may have high viscosity, low chemical and thermalstabilities, and color defect. Thus, it may be difficult to make a CLCreflective circular polarizer that can cover the visible light range byincreasing the Δn of the CLC materials. According to equation λ=np, thecenter wavelength of a reflection band of the CLC reflective circularpolarizer may be changed by changing the average refractive index n orthe pitch p of the CLC reflective circular polarizer. In someembodiments, the reflective circular polarizer may include multiplelayers, where each layer may have a different pitch and may function asa reflective circular polarizer for a different wavelength range, suchas red, green, blue, or infrared light. By stacking multiple CLC layersfor different wavelength ranges, broadband reflection of circularlypolarized light can be achieved. For example, a broadband circularpolarizer for visible light may include a stack of three CLC layers thatreflect circularly polarized light in red, green, and blue,respectively. The CLC layers may have different pitches in order toreflect circularly polarized light in different wavelength ranges asdescribed above. In some embodiments, to achieve a wide reflection band,a CLC reflective circular polarizer may be fabricated such that thepitch of the CLC is changed gradually.

FIG. 16 illustrates transmission spectra of three examples ofcholesteric liquid crystal layers having different pitches. Curve 1610shows the transmission spectrum of a first CLC circular polarizer layerthat has a relatively high reflectivity for red light. Curve 1620 showsthe transmission spectrum of a second CLC circular polarizer layer thathas a relatively high reflectivity for green light. Curve 1630 shows thetransmission spectrum of a third CLC circular polarizer layer that has ahigh reflectivity for blue light. The stack of the three CLC layers mayhave a relatively high reflectivity for light in a broad wavelengthrange. In some embodiments, circular polarizer 1508 or reflectivecircular polarizer 1514 may include a stack of CLC layers eachfunctioning as a reflective circular polarizer for a differentwavelength range.

In folded-lens system 1500, ambient light or light from the transparentdisplay may be attenuated by the circular polarizer (e.g., circularpolarizer 1508) in the see-through mode. In some embodiments, circularpolarizer 1508 may also be implemented using a CLC circular polarizer,and the folded-lens system may be set to a display mode or a see-throughmode by switching both circular polarizer 1508 and reflective circularpolarizer 1514 using voltage signals. When no voltage signal is appliedto circular polarizer 1508, folded-lens system 1500 may be set to thedisplay mode, where circular polarizer 1508 may function as a circularpolarizer as described above. When a voltage signal is applied tocircular polarizer 1508 and turns circular polarizer 1508 into atransparent device for light of any polarization state, folded-lenssystem 1500 may be set to the see-through mode, where light of anypolarization state can pass through circular polarizer 1508 with littleto no loss. As described above, in the see-through mode, reflectivecircular polarizer 1514 may also be connected to voltage source 1518,and thus may become transparent to light of any polarization state withlittle or no loss.

VII. Folded-Lens with Switchable Optical Power in Display Mode

Additionally or alternatively, two circular polarizers and a partialreflector (e.g., a 50/50 mirror) as shown in FIGS. 15A and 15B may beused to change the optical power of a folded optical device forprojecting images in different image planes. For example, when novoltage signal is applied to the circular polarizers, display light of afirst circular polarization state may pass through the first circularpolarizer and the 50/50 mirror, and reach the second circular polarizer.The second circular polarizer may reflect the light of the firstcircular polarization state back to the 50/50 mirror as described above.The 50/50 mirror may reflect the display light of the first circularpolarization state into light of a second circular polarization statethat can be transmitted by the second circular polarizer. Therefore, thefolded optical device may fold the light of the first circularpolarization state, and thus may have a first optical power for light ofthe first circular polarization state in the display light. When voltagesignals are applied to both circular polarizers (or only the secondcircular polarizer), the liquid crystal molecules in the circularpolarizers (or only the second circular polarizer) may be aligned withthe electrical field, and thus light of any polarization state can passthrough the two circular polarizers (or only the second circularpolarizer) without being folded. Thus, the folded optical device mayhave a second optical power when the voltages signals are applied. Inthis way, the folded optical device may have different optical powersand may be able to relay the displayed images on different image planes.

FIG. 17A illustrates an example of a folded-lens system 1700 configuredto operate with a first optical power according to certain embodiments.Folded-lens system 1700 may project images generated by a display 1702on different image plane. Folded-lens system 1700 may include a firstcircular polarizer 1708, a partial reflector 1710, and a second circularpolarizer 1714. In some embodiments, first circular polarizer 1708and/or second circular polarizer 1714 may be a reflective CLC circularpolarizer and may include a stack of CLC layers each functioning as acircular polarizer for a different wavelength range as described abovewith respect to FIG. 16. First circular polarizer 1708 may be controlledby voltage source 1716 and may be switchable. As shown in FIG. 17A,first circular polarizer 1708 may be disconnected from voltage source1716 and thus may function as, for example, a left-handed circularpolarizer as described above. Light from display 1702 and propagating ona first portion OP-1 of optical path 1704 may be polarized by the firstcircular polarizer 1708 and become left-handed circularly polarizedalong a second portion OP-2 of optical path 1704. After passing througha partial reflector 1710 (e.g., a 50/50 mirror), the display lightremains left-handed circularly polarized along a third portion OP-3 ofoptical path 1704. Light from third portion OP-3 of optical path 1704may reach second circular polarizer 1714.

Second circular polarizer 1714 may include a left-handed circularpolarizer and thus may reflect the left-handed circularly polarizedlight. The left-handed circularly polarized light reflected by secondcircular polarizer 1714 may propagate along a fourth portion OP-4 ofoptical path 1704 before it reaches partial reflector 1710. Partialreflector 1710 may reflect the left-handed circularly polarized lightinto right-handed circularly polarized light. The right-handedcircularly polarized light reflected off partial reflector 1710 maypropagate along a fifth portion OP-5 of optical path 1704 and reachsecond circular polarizer 1714 again. The (left-handed) second circularpolarizer 1714 may then transmit the right-handed circularly polarizedlight with little or no loss. Because light from display 1702 may travelbetween partial reflector 1710 and second circular polarizer 1714 threetimes, folded-lens system 1700 may have a first optical power and mayproject the displayed images on a first image plane.

FIG. 17B illustrates folded-lens system 1700 that is configured tooperate with a second optical power according to certain embodiments. Asshown in FIG. 17B, first circular polarizer 1708 may be connected tovoltage source 1716, and the electrical field applied to first circularpolarizer by voltage source 1716 may change the handedness of the liquidcrystal molecules such that first circular polarizer 1708 may functionas a right-handed circular polarizer when the electrical field isapplied. Light from display 1702 and propagating on an optical path 1706may be circularly polarized by first circular polarizer 1708 (nowright-handed), and may become right-handed circularly polarized alongoptical path 1706. After passing through partial reflector 1710, thedisplay light may remain right-handed circularly polarized and may reachthe left-handed second circular polarizer 1714. The (left-handed) secondcircular polarizer 1714 may transmit the right-handed circularlypolarized display light with little or no loss. Because light fromdisplay 1702 may pass through the cavity between partial reflector 1710and second circular polarizer 1714 once, folded-lens system 1700 mayhave a second optical power that is different from the first opticalpower and may project the displayed images on a second image plane.

In some embodiments, second circular polarizer 1714 may also becontrolled by a voltage source and may be switchable. For example, whenvoltage signals are applied to first circular polarizer 1708 and secondcircular polarizer 1714, both circular polarizers may transmit light ofany polarization state. Thus, folded-lens system 1700 may not fold thedisplay light and may have a second optical power different from thefirst optical power described above with respect to FIG. 17A.

In various embodiments, any of first circular polarizer 1708, partialreflector 1710, and second circular polarizer 1714 may have a flat orcurved shape. For example, any of first circular polarizer 1708, partialreflector 1710, and second circular polarizer 1714 may be formed on aflat or curved substrate. In some embodiments, any of first circularpolarizer 1708, partial reflector 1710, and second circular polarizer1714 may be formed on a surface of a lens (e.g., a concave or convexlens) as described above with respect to FIG. 8. Because the lens(es) onwhich the circular polarizers and/or the partial reflector are formedmay have a non-zero optical power, two non-zero optical powers ofdifferent values may be achieved by switching the circular polarizer(s)for projecting the displayed images on two different image planes. Insome embodiments, multiple switchable circular polarizers may be used toset the optical power of the folded-lens system to one of multiplevalues, and thus the display images may be projected on one of multipleimage planes.

VIII. Example Method

FIG. 18 is a simplified flow chart 1800 illustrating an example of amethod of displaying images at multiple image planes using one or moreswitchable circular polarizers according to certain embodiments. Theoperations described in flow chart 1800 are for illustration purposesonly and are not intended to be limiting. In various implementations,modifications may be made to flow chart 1800 to add additionaloperations, omit some operations, combine some operations, split someoperations, or reorder some operations. The operations described in flowchart 1800 may be performed using, for example, folded-lens system 800,1400, 1500, or 1700 described above.

At block 1810, a first circular polarizer (e.g., circular polarizer 1508or first circular polarizer 1708) of a folded-lens system may polarizelight from a first displayed image into light of a first circularpolarization state (e.g., left-handed circular polarization). The firstcircular polarizer may or may not be a reflective circular polarizer.For example, in some embodiments, the first circular polarizer may be aCLC reflective circular polarizer as described above. In someembodiments, the first circular polarizer may be an absorptive circularpolarizer or a different type of reflective circular polarizer.

At block 1820, a partial reflector (e.g., partial reflector 1510 or1710) of the folded-lens system may transmit the light of the firstcircular polarization state to a second circular polarizer. In someembodiments, the partial reflector may include a 50/50 mirror. In someembodiments, the partial reflector may transmit light incident from onedirection and reflect light incident from another direction. In someembodiments, the partial reflector may include a metal or glassreflector. The partial reflector may reflect polarized light and changethe polarization state of the reflected light relative to thepolarization state of the incident light.

At block 1830, the second circular polarizer (e.g., reflective polarizer1514 or second circular polarizer 1714) of the folded-lens system mayreflect the light of the first circular polarization state back to thepartial reflector. In some embodiments, the second circular polarizermay include a CLC reflective circular polarizer as described above. Thesecond circular polarizer may reflect the light of the first circularpolarization state (e.g., left-handed circular polarization) withoutchanging the handedness of the reflected light, and may transmit lightof the opposite circular polarization state (e.g., right-handed circularpolarization) without changing the handedness of the transmitted light.

At block 1840, the partial reflector may reflect the light of the firstcircular polarization state into light of a second circular polarizationstate back to the second circular polarizer. For example, if the lightof the first circular polarization state is left-handed circularlypolarized, the light reflected off the partial reflector may beright-handed circularly polarized.

At block 1850, the second circular polarizer may transmit the light ofthe second circular polarization state to a user's eye. For example, thesecond circular polarizer may include left-handed CLC helixes and mayfunction as a left-handed reflective circular polarizer that cantransmit right-handed circularly polarized light with little or no loss.Because the light from the first image travels in the cavity between thepartial reflector and the second circular polarizer three times, theoptical path for the light from the first image may be longer than thephysical path of the folded-lens system. Thus, the folded-lens systemmay have a large optical power and may relay the first image to a firstimage plane.

At block 1860, a voltage source may apply a voltage signal on the secondcircular polarizer. The voltage signal may cause the second circularpolarizer to transmit light of any circular polarization. For example,as described above, the electric field applied to the second circularpolarizer by the voltage source may realign the liquid crystal moleculesin the CLC circular polarizer with the direction of the electric fieldand disrupt the helical structure, and thus the second circularpolarizer may become transparent to light of any polarization state.

At block 1870, the second circular polarizer may transmit light from asecond image to the user's eye. In some embodiments, the first circularpolarizer may polarize the light from the second image into light of thefirst circular polarization state; the partial reflector may transmitthe light of the first circular polarization state in the light from thesecond image to the second circular polarizer; and the second circularpolarizer (transparent to light of any polarization state afterreceiving the voltage signal) may transmit the light of the firstcircular polarization state in the light from the second image to theuser's eye. In some embodiments, a second voltage source may apply asecond voltage signal on the first circular polarizer, where the secondvoltage signal may cause the first circular polarizer to becometransparent to light of any circular polarization state. Thus, the firstcircular polarizer and the partial reflector may transmit the light inany polarization state from the second image to the second circularpolarizer, which may transmit light of any circular polarization statefrom the second image to the user's eye. In either case, the light fromthe second image may travel in the cavity between the partial reflectorand the second circular polarizer only once, and the optical path forthe light from the second image may be similar to the physical path ofthe folded-lens system. Thus, the folded-lens system may have a smalloptical power and may relay the second image to a second image planedifferent from the first image plane.

FIG. 19 is a simplified flow chart 1900 illustrating an example of amethod of operating a near-eye display device in a display mode and asee-through mode according to certain embodiments. The operationsdescribed in flow chart 1900 are for illustration purposes only and arenot intended to be limiting. In various implementations, modificationsmay be made to flow chart 1900 to add additional operations, omit someoperations, combine some operations, split some operations, or reordersome operations. The operations described in flow chart 1900 may beperformed using, for example, folded-lens system 800, 1400, 1500, or1700 described above.

At block 1910, a first circular polarizer (e.g., reflective polarizer1514 or second circular polarizer 1714) of a folded-lens system (e.g.,folded-lens system 1500 or 1700) in the near-eye display device may bedisconnected from a voltage signal to set the near-eye display device tothe display mode. As described above, the first circular polarizer mayinclude a CLC reflective circular polarizer that includes a CLC helicalstructure when no voltage signal is applied to it. The circularpolarization capability of the first circular polarizer may be disabledwhen a voltage signal is applied to it to realign the liquid crystalmolecules and disrupt the helical structure. When no voltage signal isapplied, the first circular polarizer may reflect light of a firstcircular polarization state (e.g., right-handed circular polarization ifthe helical structure is right-handed) without changing the polarizationstate of the reflected light, and may transmit light of a secondcircular polarization state (e.g., left-handed circular polarization)without changing the polarization state of the transmitted light.

At block 1920, a second circular polarizer (e.g., circular polarizer1508 or first circular polarizer 1708) of the folded-lens system maypolarize light from a displayed image into light of a first circularpolarization state (e.g., right-handed circular polarization). In someembodiments, the first circular polarizer may be a CLC reflectivecircular polarizer as described above. In some embodiments, the firstcircular polarizer may be an absorptive circular polarizer or adifferent type of reflective circular polarizer.

At block 1930, a partial reflector (e.g., partial reflector 1510 or1710) of the folded-lens system may transmit the light of the firstcircular polarization state to the first circular polarizer. In someembodiments, the partial reflector may include a 50/50 mirror. In someembodiments, the partial reflector may transmit light incident from onedirection and reflect light incident from another direction. In someembodiments, the partial reflector may include a metal or glassreflector. The partial reflector may reflect polarized light and changethe polarization state of the reflected light relative to thepolarization state of the incident light.

At block 1940, the first circular polarizer may reflect the light of thefirst circular polarization state back to the partial reflector. Forexample, if the light of the first circular polarization state isright-handed circularly polarized, the light reflected off the firstcircular polarizer may also be right-handed circularly polarized.

At block 1950, the partial reflector may reflect the light of the firstcircular polarization state into light of a second circular polarizationstate back to the first circular polarizer. For example, if the light ofthe first circular polarization state is right-handed circularlypolarized, the light reflected off the partial reflector may beleft-handed circularly polarized.

At block 1960, the first circular polarizer may transmit the light ofthe second circular polarization state to a user's eye. For example, thefirst circular polarizer may be a right-handed circular polarizer andmay transmit the left-handed circularly polarized light reflected offthe partial reflector to user's eye. Because the light from thedisplayed image travels in the cavity between the partial reflector andthe first circular polarizer three times in the display mode, thefolded-lens system may have a large optical power and may relay thedisplayed image to an image plane.

At block 1970, the first circular polarizer may be connected to thevoltage signal, where the voltage signal may cause the first circularpolarizer to transmit light of any circular polarization state and thusset the near-eye display device to the see-through mode. For example, asdescribed above, the electric field applied in the first circularpolarizer by the voltage signal may realign the liquid crystal moleculesin the CLC circular polarizer with the direction of the electric fieldand disrupt the helical structure, and thus the first circular polarizermay become transparent to light of any polarization state.

At block 1980, the first circular polarizer may transmit ambient lightto the user's eye. In some embodiments, the second circular polarizermay polarize the ambient light into light of the first circularpolarization state, the partial reflector may transmit the light of thefirst circular polarization state in the ambient light to the firstcircular polarizer, and the first circular polarizer may then transmitthe light of the first circular polarization state in the ambient lightto the user's eye. In some embodiments, a second voltage signal may beapplied on the second circular polarizer, where the second voltagesignal may disrupt the helical structure and cause the second circularpolarizer to become transparent to light of any circular polarizationstate. Thus, the second circular polarizer and the partial reflector maytransmit ambient light of any circular polarization state to the firstcircular polarizer, and the first circular polarizer may then transmitthe ambient light of any circular polarization state to the user's eye.Therefore, in the see-through mode, the ambient light may travel throughthe cavity between the partial reflector and the second circularpolarizer only once, and thus the folded-lens system may have a small ornear-zero optical power for ambient light.

Embodiments of the invention may be used to fabricate components of anartificial reality system or may be implemented in conjunction with anartificial reality system. Artificial reality is a form of reality thathas been adjusted in some manner before presentation to a user, whichmay include, for example, a virtual reality (VR), an augmented reality(AR), a mixed reality (MR), a hybrid reality, or some combination and/orderivatives thereof. Artificial reality content may include completelygenerated content or generated content combined with captured (e.g.,real-world) content. The artificial reality content may include video,audio, haptic feedback, or some combination thereof, and any of whichmay be presented in a single channel or in multiple channels (such asstereo video that produces a three-dimensional effect to the viewer).Additionally, in some embodiments, artificial reality may also beassociated with applications, products, accessories, services, or somecombination thereof, that are used to, for example, create content in anartificial reality and/or are otherwise used in (e.g., performactivities in) an artificial reality. The artificial reality system thatprovides the artificial reality content may be implemented on variousplatforms, including a head-mounted display (HMD) connected to a hostcomputer system, a standalone HMD, a mobile device or computing system,or any other hardware platform capable of providing artificial realitycontent to one or more viewers.

IX. Example System

FIG. 20 is a simplified block diagram of an example of an electronicsystem 2000 of a near-eye display (e.g., HMD device) for implementingsome of the examples disclosed herein. Electronic system 2000 may beused as the electronic system of an HMD device or other near-eyedisplays described above. In this example, electronic system 2000 mayinclude one or more processor(s) 2010 and a memory 2020. Processor(s)2010 may be configured to execute instructions for performing operationsat a number of components, and can be, for example, a general-purposeprocessor or microprocessor suitable for implementation within aportable electronic device. Processor(s) 2010 may be communicativelycoupled with a plurality of components within electronic system 2000. Torealize this communicative coupling, processor(s) 2010 may communicatewith the other illustrated components across a bus 2040. Bus 2040 may beany subsystem adapted to transfer data within electronic system 2000.Bus 2040 may include a plurality of computer buses and additionalcircuitry to transfer data.

Memory 2020 may be coupled to processor(s) 2010. In some embodiments,memory 2020 may offer both short-term and long-term storage and may bedivided into several units. Memory 2020 may be volatile, such as staticrandom access memory (SRAM) and/or dynamic random access memory (DRAM)and/or non-volatile, such as read-only memory (ROM), flash memory, andthe like. Furthermore, memory 2020 may include removable storagedevices, such as secure digital (SD) cards. Memory 2020 may providestorage of computer-readable instructions, data structures, programmodules, and other data for electronic system 2000. In some embodiments,memory 2020 may be distributed into different hardware modules. A set ofinstructions and/or code might be stored on memory 2020. Theinstructions might take the form of executable code that may beexecutable by electronic system 2000, and/or might take the form ofsource and/or installable code, which, upon compilation and/orinstallation on electronic system 2000 (e.g., using any of a variety ofgenerally available compilers, installation programs,compression/decompression utilities, etc.), may take the form ofexecutable code.

In some embodiments, memory 2020 may store a plurality of applicationmodules 2022 through 2024, which may include any number of applications.Examples of applications may include gaming applications, conferencingapplications, video playback applications, or other suitableapplications. The applications may include a depth sensing function oreye tracking function. Application modules 2022-2024 may includeparticular instructions to be executed by processor(s) 2010. In someembodiments, certain applications or parts of application modules2022-2024 may be executable by other hardware modules 2080. In certainembodiments, memory 2020 may additionally include secure memory, whichmay include additional security controls to prevent copying or otherunauthorized access to secure information.

In some embodiments, memory 2020 may include an operating system 2025loaded therein. Operating system 2025 may be operable to initiate theexecution of the instructions provided by application modules 2022-2024and/or manage other hardware modules 2080 as well as interfaces with awireless communication subsystem 2030 which may include one or morewireless transceivers. Operating system 2025 may be adapted to performother operations across the components of electronic system 2000including threading, resource management, data storage control and othersimilar functionality.

Wireless communication subsystem 2030 may include, for example, aninfrared communication device, a wireless communication device and/orchipset (such as a Bluetooth® device, an IEEE 802.11 device, a Wi-Fidevice, a WiMax device, cellular communication facilities, etc.), and/orsimilar communication interfaces. Electronic system 2000 may include oneor more antennas 2034 for wireless communication as part of wirelesscommunication subsystem 2030 or as a separate component coupled to anyportion of the system. Depending on desired functionality, wirelesscommunication subsystem 2030 may include separate transceivers tocommunicate with base transceiver stations and other wireless devicesand access points, which may include communicating with different datanetworks and/or network types, such as wireless wide-area networks(WWANs), wireless local area networks (WLANs), or wireless personal areanetworks (WPANs). A WWAN may be, for example, a WiMax (IEEE 802.16)network. A WLAN may be, for example, an IEEE 802.11x network. A WPAN maybe, for example, a Bluetooth network, an IEEE 802.15x, or some othertypes of network. The techniques described herein may also be used forany combination of WWAN, WLAN, and/or WPAN. Wireless communicationssubsystem 2030 may permit data to be exchanged with a network, othercomputer systems, and/or any other devices described herein. Wirelesscommunication subsystem 2030 may include a means for transmitting orreceiving data, such as identifiers of HMD devices, position data, ageographic map, a heat map, photos, or videos, using antenna(s) 2034 andwireless link(s) 2032. Wireless communication subsystem 2030,processor(s) 2010, and memory 2020 may together comprise at least a partof one or more of a means for performing some functions disclosedherein.

Embodiments of electronic system 2000 may also include one or moresensors 2090. Sensor(s) 2090 may include, for example, an image sensor,an accelerometer, a pressure sensor, a temperature sensor, a proximitysensor, a magnetometer, a gyroscope, an inertial sensor (e.g., a modulethat combines an accelerometer and a gyroscope), an ambient lightsensor, or any other similar module operable to provide sensory outputand/or receive sensory input, such as a depth sensor or a positionsensor. For example, in some implementations, sensor(s) 2090 may includeone or more inertial measurement units (IMUs) and/or one or moreposition sensors. An IMU may generate calibration data indicating anestimated position of the HMD device relative to an initial position ofthe HMD device, based on measurement signals received from one or moreof the position sensors. A position sensor may generate one or moremeasurement signals in response to motion of the HMD device. Examples ofthe position sensors may include, but are not limited to, one or moreaccelerometers, one or more gyroscopes, one or more magnetometers,another suitable type of sensor that detects motion, a type of sensorused for error correction of the IMU, or some combination thereof. Theposition sensors may be located external to the IMU, internal to theIMU, or some combination thereof. At least some sensors may use astructured light pattern for sensing.

Electronic system 2000 may include a display module 2060. Display module2060 may be a near-eye display, and may graphically present information,such as images, videos, and various instructions, from electronic system2000 to a user. Such information may be derived from one or moreapplication modules 2022-2024, virtual reality engine 2026, one or moreother hardware modules 2080, a combination thereof, or any othersuitable means for resolving graphical content for the user (e.g., byoperating system 2025). Display module 2060 may use liquid crystaldisplay (LCD) technology, light-emitting diode (LED) technology(including, for example, OLED, ILED, mLED, AMOLED, TOLED, etc.), lightemitting polymer display (LPD) technology, or some other displaytechnology.

Electronic system 2000 may include a user input/output module 2070. Userinput/output module 2070 may allow a user to send action requests toelectronic system 2000. An action request may be a request to perform aparticular action. For example, an action request may be to start or endan application or to perform a particular action within the application.User input/output module 2070 may include one or more input devices.Example input devices may include a touchscreen, a touch pad,microphone(s), button(s), dial(s), switch(es), a keyboard, a mouse, agame controller, or any other suitable device for receiving actionrequests and communicating the received action requests to electronicsystem 2000. In some embodiments, user input/output module 2070 mayprovide haptic feedback to the user in accordance with instructionsreceived from electronic system 2000. For example, the haptic feedbackmay be provided when an action request is received or has beenperformed.

Electronic system 2000 may include a camera 2050 that may be used totake photos or videos of a user, for example, for tracking the user'seye position. Camera 2050 may also be used to take photos or videos ofthe environment, for example, for VR, AR, or MR applications. Camera2050 may include, for example, a complementary metal-oxide-semiconductor(CMOS) image sensor with a few millions or tens of millions of pixels.In some implementations, camera 2050 may include two or more camerasthat may be used to capture 3-D images.

In some embodiments, electronic system 2000 may include a plurality ofother hardware modules 2080. Each of other hardware modules 2080 may bea physical module within electronic system 2000. While each of otherhardware modules 2080 may be permanently configured as a structure, someof other hardware modules 2080 may be temporarily configured to performspecific functions or temporarily activated. Examples of other hardwaremodules 2080 may include, for example, an audio output and/or inputmodule (e.g., a microphone or speaker), a near field communication (NFC)module, a rechargeable battery, a battery management system, awired/wireless battery charging system, etc. In some embodiments, one ormore functions of other hardware modules 2080 may be implemented insoftware.

In some embodiments, memory 2020 of electronic system 2000 may alsostore a virtual reality engine 2026. Virtual reality engine 2026 mayexecute applications within electronic system 2000 and receive positioninformation, acceleration information, velocity information, predictedfuture positions, or some combination thereof of the HMD device from thevarious sensors. In some embodiments, the information received byvirtual reality engine 2026 may be used for producing a signal (e.g.,display instructions) to display module 2060. For example, if thereceived information indicates that the user has looked to the left,virtual reality engine 2026 may generate content for the HMD device thatmirrors the user's movement in a virtual environment. Additionally,virtual reality engine 2026 may perform an action within an applicationin response to an action request received from user input/output module2070 and provide feedback to the user. The provided feedback may bevisual, audible, or haptic feedback. In some implementations,processor(s) 2010 may include one or more GPUs that may execute virtualreality engine 2026.

In various implementations, the above-described hardware and modules maybe implemented on a single device or on multiple devices that cancommunicate with one another using wired or wireless connections. Forexample, in some implementations, some components or modules, such asGPUs, virtual reality engine 2026, and applications (e.g., trackingapplication), may be implemented on a console separate from thehead-mounted display device. In some implementations, one console may beconnected to or support more than one HMD.

In alternative configurations, different and/or additional componentsmay be included in electronic system 2000. Similarly, functionality ofone or more of the components can be distributed among the components ina manner different from the manner described above. For example, in someembodiments, electronic system 2000 may be modified to include othersystem environments, such as an AR system environment and/or an MRenvironment.

The methods, systems, and devices discussed above are examples. Variousembodiments may omit, substitute, or add various procedures orcomponents as appropriate. For instance, in alternative configurations,the methods described may be performed in an order different from thatdescribed, and/or various stages may be added, omitted, and/or combined.Also, features described with respect to certain embodiments may becombined in various other embodiments. Different aspects and elements ofthe embodiments may be combined in a similar manner. Also, technologyevolves and, thus, many of the elements are examples that do not limitthe scope of the disclosure to those specific examples.

Specific details are given in the description to provide a thoroughunderstanding of the embodiments. However, embodiments may be practicedwithout these specific details. For example, well-known circuits,processes, systems, structures, and techniques have been shown withoutunnecessary detail in order to avoid obscuring the embodiments. Thisdescription provides example embodiments only, and is not intended tolimit the scope, applicability, or configuration of the invention.Rather, the preceding description of the embodiments will provide thoseskilled in the art with an enabling description for implementing variousembodiments. Various changes may be made in the function and arrangementof elements without departing from the spirit and scope of the presentdisclosure.

Also, some embodiments were described as processes depicted as flowdiagrams or block diagrams. Although each may describe the operations asa sequential process, many of the operations may be performed inparallel or concurrently. In addition, the order of the operations maybe rearranged. A process may have additional steps not included in thefigure. Furthermore, embodiments of the methods may be implemented byhardware, software, firmware, middleware, microcode, hardwaredescription languages, or any combination thereof. When implemented insoftware, firmware, middleware, or microcode, the program code or codesegments to perform the associated tasks may be stored in acomputer-readable medium such as a storage medium. Processors mayperform the associated tasks.

It will be apparent to those skilled in the art that substantialvariations may be made in accordance with specific requirements. Forexample, customized or special-purpose hardware might also be used,and/or particular elements might be implemented in hardware, software(including portable software, such as applets, etc.), or both. Further,connection to other computing devices such as network input/outputdevices may be employed.

With reference to the appended figures, components that can includememory can include non-transitory machine-readable media. The term“machine-readable medium” and “computer-readable medium” may refer toany storage medium that participates in providing data that causes amachine to operate in a specific fashion. In embodiments providedhereinabove, various machine-readable media might be involved inproviding instructions/code to processing units and/or other device(s)for execution. Additionally or alternatively, the machine-readable mediamight be used to store and/or carry such instructions/code. In manyimplementations, a computer-readable medium is a physical and/ortangible storage medium. Such a medium may take many forms, including,but not limited to, non-volatile media, volatile media, and transmissionmedia. Common forms of computer-readable media include, for example,magnetic and/or optical media such as compact disk (CD) or digitalversatile disk (DVD), punch cards, paper tape, any other physical mediumwith patterns of holes, a RAM, a programmable read-only memory (PROM),an erasable programmable read-only memory (EPROM), a FLASH-EPROM, anyother memory chip or cartridge, a carrier wave as described hereinafter,or any other medium from which a computer can read instructions and/orcode. A computer program product may include code and/ormachine-executable instructions that may represent a procedure, afunction, a subprogram, a program, a routine, an application (App), asubroutine, a module, a software package, a class, or any combination ofinstructions, data structures, or program statements.

Those of skill in the art will appreciate that information and signalsused to communicate the messages described herein may be representedusing any of a variety of different technologies and techniques. Forexample, data, instructions, commands, information, signals, bits,symbols, and chips that may be referenced throughout the abovedescription may be represented by voltages, currents, electromagneticwaves, magnetic fields or particles, optical fields or particles, or anycombination thereof.

Terms, “and” and “or” as used herein, may include a variety of meaningsthat are also expected to depend at least in part upon the context inwhich such terms are used. Typically, “or” if used to associate a list,such as A, B, or C, is intended to mean A, B, and C, here used in theinclusive sense, as well as A, B, or C, here used in the exclusivesense. In addition, the term “one or more” as used herein may be used todescribe any feature, structure, or characteristic in the singular ormay be used to describe some combination of features, structures, orcharacteristics. However, it should be noted that this is merely anillustrative example and claimed subject matter is not limited to thisexample. Furthermore, the term “at least one of” if used to associate alist, such as A, B, or C, can be interpreted to mean any combination ofA, B, and/or C, such as A, AB, AC, BC, AA, ABC, AAB, AABBCCC, etc.

Further, while certain embodiments have been described using aparticular combination of hardware and software, it should be recognizedthat other combinations of hardware and software are also possible.Certain embodiments may be implemented only in hardware, or only insoftware, or using combinations thereof. In one example, software may beimplemented with a computer program product containing computer programcode or instructions executable by one or more processors for performingany or all of the steps, operations, or processes described in thisdisclosure, where the computer program may be stored on a non-transitorycomputer readable medium. The various processes described herein can beimplemented on the same processor or different processors in anycombination.

Where devices, systems, components or modules are described as beingconfigured to perform certain operations or functions, suchconfiguration can be accomplished, for example, by designing electroniccircuits to perform the operation, by programming programmableelectronic circuits (such as microprocessors) to perform the operationsuch as by executing computer instructions or code, or processors orcores programmed to execute code or instructions stored on anon-transitory memory medium, or any combination thereof. Processes cancommunicate using a variety of techniques, including, but not limitedto, conventional techniques for inter-process communications, anddifferent pairs of processes may use different techniques, or the samepair of processes may use different techniques at different times.

The specification and drawings are, accordingly, to be regarded in anillustrative rather than a restrictive sense. It will, however, beevident that additions, subtractions, deletions, and other modificationsand changes may be made thereunto without departing from the broaderspirit and scope as set forth in the claims. Thus, although specificembodiments have been described, these are not intended to be limiting.Various modifications and equivalents are within the scope of thefollowing claims.

What is claimed is:
 1. An optical device comprising: a first polarizerconfigured to polarize incident light into light of a first circularpolarization state; a second polarizer; and a partial reflectorpositioned between the first polarizer and the second polarizer,wherein: the partial reflector is configured to transmit the light ofthe first circular polarization state from the first polarizer; thesecond polarizer is configured to reflect the light of the firstcircular polarization state, wherein the reflected light from the secondpolarizer is in the first circular polarization state; the partialreflector is further configured to reflect the reflected light from thesecond polarizer, wherein the light reflected by the partial reflectorincludes light in a second circular polarization state different fromthe first circular polarization state; and the second polarizer isfurther configured to transmit the light in the second circularpolarization state and maintain the second circular polarization stateof the transmitted light.
 2. The optical device of claim 1, wherein atleast one of the first polarizer, the second polarizer, or the partialreflector is on a curved surface.
 3. The optical device of claim 2,wherein the curved surface is a surface of an optical lens.
 4. Theoptical device of claim 1, wherein the second polarizer includes acholesteric liquid crystal (CLC) circular polarizer, the CLC circularpolarizer including liquid crystal molecules arranged in a helicalstructure.
 5. The optical device of claim 4, wherein the helicalstructure includes two or more pitches.
 6. The optical device of claim4, wherein the CLC circular polarizer includes a plurality of layers,each layer having a different reflection wavelength range.
 7. Theoptical device of claim 6, wherein each of the plurality of layersincludes a helical structure having a different pitch.
 8. The opticaldevice of claim 7, wherein at least two layers of the plurality oflayers are doped with a chiral dopant material at different dopantconcentrations.
 9. The optical device of claim 7, wherein at least twolayers of the plurality of layers are doped with different chiral dopantmaterials.
 10. The optical device of claim 4, wherein a pitch of thehelical structure varies gradually.
 11. The optical device of claim 4,wherein the CLC circular polarizer includes double-twist cholestericliquid crystal layers or liquid crystal polymer layers.
 12. The opticaldevice of claim 4, wherein: the helical structure includes a left-handedhelical structure; and the second polarizer is configured to transmitright-handed circularly polarized light and reflect left-handedcircularly polarized light.
 13. The optical device of claim 4, wherein:the helical structure includes a right-handed helical structure; and thesecond polarizer is configured to transmit left-handed circularlypolarized light and reflect right-handed circularly polarized light. 14.The optical device of claim 1, wherein the first polarizer includes acholesteric liquid crystal (CLC) circular polarizer, the CLC circularpolarizer including liquid crystal molecules arranged in a helicalstructure.
 15. A method of displaying images, the method comprising:polarizing, by a first polarizer, light from an image source into lightof a first circular polarization state; transmitting, by a partialreflector, the light of the first circular polarization state to asecond polarizer; reflecting, by the second polarizer, the light of thefirst circular polarization state back to the partial reflector, whereinthe reflected light is in the first circular polarization state;reflecting, by the partial reflector, the light of the first circularpolarization state into light of a second circular polarization stateback to the second polarizer; and transmitting, by the second polarizer,the light of the second circular polarization state to a user's eye,wherein the light transmitted to the user's eye maintains the secondcircular polarization state.
 16. The method of claim 15, wherein thesecond polarizer includes a cholesteric liquid crystal (CLC) reflectivecircular polarizer.
 17. A near-eye display device comprising: a displayconfigured to emit display light; a first polarizer configured topolarize the display light into light of a first circular polarizationstate; a second polarizer; and a partial reflector positioned betweenthe first polarizer and the second polarizer, wherein: the partialreflector is configured to transmit the light of the first circularpolarization state from the first polarizer; the second polarizer isconfigured to reflect the light of the first circular polarization statewithout changing its polarization state; the partial reflector isfurther configured to reflect the light reflected from the secondpolarizer, wherein the light reflected by the partial reflector includeslight in a second circular polarization state different from the firstcircular polarization state; and the second polarizer is furtherconfigured to transmit the light in the second circular polarizationstate to a user's eye, wherein the light transmitted to the user's eyemaintains the second circular polarization state.
 18. The near-eyedisplay device of claim 17, further comprising an optical lens having anon-zero optical power, wherein at least one of the first polarizer, thesecond polarizer, or the partial reflector is on a surface of theoptical lens.
 19. The near-eye display device of claim 17, wherein: thedisplay includes a transparent display configured to transmit ambientlight; and the near-eye display device is configured to transmit boththe ambient light and the display light to the user's eye.
 20. Thenear-eye display device of claim 17, wherein the second polarizerincludes a cholesteric liquid crystal (CLC) reflective circularpolarizer.
 21. A near-eye display device comprising: a display includingan output surface, wherein: the display is configured to emit displaylight through the output surface; and the output surface is configuredto at least partially reflect light incident on the output surface froman exterior of the display, wherein the partially reflected light andthe light incident on the output surface from the exterior of thedisplay have different polarization states; and a reflective circularpolarizer formed on the output surface of the display and includingliquid crystal molecules arranged in a helical structure, the reflectivecircular polarizer configured to: reflect light of a first circularpolarization state in the display light back to the output surface ofthe display, wherein the reflected light from the reflective circularpolarizer to the output surface of the display is in the first circularpolarization state; and transmit light of a second circular polarizationstate in the display light to a user's eye, wherein the lighttransmitted to the user's eye maintains the second circular polarizationstate.